Modern River-Sand Geochemical Mapping in the Manufahi Municipality and Its Surroundings, Timor-Leste: Implications for Provenance

Abstract

A geochemical mapping of regional modern river-sand is performed to clarify geological information in the study area of Timor-Leste. Several areas of Timor-Leste including the study area in particular have limited geological information due to limited accessibility and dense vegetation coverage, and deformed, weathered, and erosion-covered materials. A total of 53 modern river sand samples were collected and analyzed. Ten major elements were determined by using wavelength-dispersive X-ray fluorescence. Areas characterized by clastic sedimentary rocks are recognized clearly by elevated concentrations of SiO₂, Al₂O₃, and K₂O. Meanwhile, areas covered by carbonate sedimentary rocks are detected by significant concentrations of CaO and MnO. The occurrences of the altered clastic and carbonate sedimentary rocks of the Wailuli and Aitutu Formations due to metamorphic, silicification and other alteration processes were responsible for the elevated concentrations and positive correlation between SiO₂, CaO, K₂O, and MnO, and CaO, TiO₂, and MnO in the midstream and near the downstream areas of the Clerec and Sahe River catchments. The positive correlation observed between TiO₂, CaO and MnO may be ascribed to the presence of carbonate components associated with secondary Ti-bearing minerals, which are potentially formed through hydrothermal alteration processes.

1. Introduction

Timor-Leste is a relatively new independent country. It officially gained its independence in 2002. Timor-Leste is located between Southeast Asia and the Pacific region, surrounded by Indonesia’s islands, with the western part of the island of Timor shared with Indonesian territory and Australia as its southern neighbor across the Timor Sea (Figure 1A).

Since Portuguese colonization, the geology of Timor-Leste has been studied and mapped. The majority of geological research studies conducted in the territory of Timor-Leste have been concerned with prospecting and discovering oil and natural gas, paleontology, tectonic settings, and stratigraphy [1,2,3,4,5,6,7,8,9,10,11,12]. However, geochemical mapping studies have not yet been conducted in the majority of the Timor-Leste territory, including the study area.

Timor island is located in a zone where the Australian and the Eurasian plates collide, and it is characterized by active tectonics. This zone has led to the uplifting of land, formation of the landscape, mountain-building processes, installation of overthrust sheets, complex lithological formations, and other geological phenomena and processes within Timor Island. The terrain of the island is characterized by a rugged topography with steep slopes, large mountains, high peaks, and deep valleys. External geodynamic processes such as erosion and weathering also contribute to landscape shaping. The lithologic formations installed and deposited on Timor Island are largely composed of non-volcanic strata that range in age from Permian to Quaternary. Tectonically, these formations can be classified into allochthonous, para-autochthonous, and autochthonous units, and are similar to the Asian and Australian successions. Some of these formations have been involved in various geological events and tectonic processes, such as deformation, metamorphism, volcanic activity, mineralization, and hydrothermal alterations, before and after the orogenic phase, which occurred from the Late Jurassic to the Middle Miocene [7,9,13,14,15,16,17,18,19,20].

Figure 1. Showing: (A) the geographical location of Timor-Leste and plate tectonic and boundaries of the Southeast Asia. The Sunda (SU), Australia (AU), Timor (TI), Banda Sea (BS), Molucca Sea (MS), Bird’s Head (BH), Philippine Sea (PS), Caroline (CL), Woodlark (WL), and Maoke (MO) boundaries are marked with bold greyish black lines [21,22,23]. (B) geographical location of the study area and its surroundings. Heavy black lines represent the boundaries of Timor-Leste municipalities. LA = Lautem; BA = Baucau; VI = Viqueque; MT = Manatutu; AL = Aileu; MF = Manufahi; AN = Ainaro; and CO = Covalima [23]. (C) river-sand sampling point distributions with drainage basins and geological formations [24,25] in the study area.

Figure 1. Showing: (A) the geographical location of Timor-Leste and plate tectonic and boundaries of the Southeast Asia. The Sunda (SU), Australia (AU), Timor (TI), Banda Sea (BS), Molucca Sea (MS), Bird’s Head (BH), Philippine Sea (PS), Caroline (CL), Woodlark (WL), and Maoke (MO) boundaries are marked with bold greyish black lines [21,22,23]. (B) geographical location of the study area and its surroundings. Heavy black lines represent the boundaries of Timor-Leste municipalities. LA = Lautem; BA = Baucau; VI = Viqueque; MT = Manatutu; AL = Aileu; MF = Manufahi; AN = Ainaro; and CO = Covalima [23]. (C) river-sand sampling point distributions with drainage basins and geological formations [24,25] in the study area.

In this work, the studied sediment samples are referred to as river sands [26,27,28,29,30,31]. River sand samples were collected from the active channel below the water level and were dominated by fine to coarse sand fractions. Modern river sands are composite products of the weathering and erosion of rocks, minerals, and soils from upstream of the sampling site. These sediments are transported and deposited by stream water flow within a river catchment area [32,33,34,35,36].

Modern river sands were used as samples in our geochemical mapping study due to the source rocks’ original geochemical signatures may still be detectable [37,38,39]. The chemical compositions of modern river sands are largely influenced by source rocks from underlying lithologies within a drainage basin [40,41,42,43,44]. However, these compositions are also affected by several factors such as the occurrence of mineral deposits, topographic relief, climate, transportation, sedimentation, and depositional environment [27,34,45,46,47,48,49]. In addition, in the last few years, modern river sands have been used as a sampling medium by numerous researchers in geochemical mapping investigations, particularly focused on the study of provenance [50,51,52,53,54,55,56] and mineral exploration [57,58,59,60].

The majority of Timor-Leste’s land surface and study area in particular are covered by light to dense vegetation and weathered and eroded materials. Direct field geological mapping in these regions may also influence lithological identification capability, especially in characterizing more than one type of source or rock unit [61]. This study demonstrated the potential of river sand geochemical mapping as a lithological mapping tool. It started from the research area; this study must lead to a future national project establishing a geochemical map of the country that can be utilized for environmental studies, mineral resource discovery, and lithological mapping all over the country. This study aimed to establish a geochemical database for a limited area of Timor-Leste and to discuss its characteristics and the relationship with the geology of the study area.

2. Geographical and Geological Setting of Timor-Leste and the Study Area

Officially known as Timor-Leste, the eastern portion of Timor encompasses the island of Atauro to the north, the islet of Jaco to the east, and the enclave of Oecusse, which is bordered by Indonesian West Timor, to the west (Figure 1A,B).

The study area is located in the municipality of Manufahi and its surroundings on the southern coast of Timor-Leste. The Timor Sea forms the southern border, while Manatuto, Aileu, and Ainaro Municipalities form the eastern, northern, and western borders, respectively (Figure 1B). The study area comprises a region of rugged mountainous topography characterized by varying slopes, ranging from almost flat to very steep. Here, it is possible to observe the activities of external geodynamic processes, such as erosion and weathering. The highest elevations are found in the eastern and northern parts of the territory; the highest peak is at Cablac Mountain, with a height of up to 2085 m.

Timor Island, the islet of Jaco, and several other islands in the southeastern region of the Indonesian archipelago are part of the Outer Banda Arc System because of their position in a complex tectonic setting, where two major plates, the Australian and Eurasian plates, collide. Timor Island is characterized by tectonic and geological features, including the predominance of Permian to Cretaceous sedimentary rocks with affinities to Australian and Asian geological sequences that have undergone significant deformation, resulting in complex structures, faulting, and folding. In contrast, the small island of Atauro is located in the Banda Sea between Timor and Wetar, is linked to the Inner Banda Arc, an area of geological interest due to its volcanic and tectonic characteristics, which are associated with subduction-related processes [2,6,10,11,19,62,63,64,65,66,67].

There are five tectonostratigraphic units on the island of Timor [9,68,69,70], which can be summarized as follows: (1) the Gondwana megasequence is largely composed of allochthonous and para-autochthonous sedimentary rocks from pre-rift sequences that were deposited on the northeastern shelf of the Gondwana continent, and its age ranges from the Permian to the Middle Jurassic; (2) the Australian-margin megasequence is mostly composed of para-autochthonous sedimentary rocks of the marine environment from post-rift sequences that were deposited on the plateau near the Australian mainland. Its age ranges from the Middle Jurassic to the Middle Miocene, and the initiation of the post-rift sequence deposition at 155 Ma is associated with a significant tectonic event, which is indicated by a break-up unconformity; (3) the Banda Terrane units are characterized by Cenozoic igneous rocks and their cover sediments as well as Mesozoic metamorphic basements that are exposed as thrust sheets and emplaced onto Timor-Leste during the collision phase. They are believed to be derived from the Banda Arc and its forearc arc, as well as components of the crustal blocks of Australia; (4) the Synorogenic Mélange is primarily composed of a matrix rich in scaly clay that is derived from mudrock-rich pre- and post-rift successions. Tectonic processes have transported and reassembled this sequence into a chaotic mixture; and (5) the Synorogenic megasequence is characterized by autochthonous sedimentary successions installed through uplifting processes and deposited from eroded sediments of existing rocks in the surrounding basin and depressions during the latest Miocene to the Holocene.

The five tectonostratigraphic units are well-preserved from north to south in the study area (Figure 1C), and the contact between these units is a fault and/or unconformity [1,9,14,16,63,68,69,70,71]. In the northern to central parts of the study area, the Banda Terrane and its sedimentary cover units were emplaced above the Synorogenic Mélange and Gondwana Megasequences. In the southern part, Synorogenic Megasequences were deposited above the Australian-Margin Megasequences during the latest Miocene to Holocene.

According to Bachri and Situmorang [24], Partoyo et al. [25], and the geological research conducted by Audley-Charles [1,14] and others [3,9,18,20,72,73,74,75,76,77,78,79], the study area consists of the following formations (Figure 1C).

(a)

Pleistocene–Holocene Suai Formation

It is mostly composed of rudites and arenites, with minor amounts of mud and marls. The particles of the formation were mostly sourced from the Viqueque Formation, Dilor Conglomerate, and Lolotoi Complex. This formation belongs to the Synorogenic Megasequence.

(b)

Pleistocene–Holocene Ainaro Formation (Ainaro Gravels)

This formation is part of the Synorogenic Megasequence and is primarily composed of matrix-supported conglomerates that are believed to be sediments from an ancient river terrace. Occasionally, calcite lateritic cements fill these sediments, and the irregular surfaces of the river terrace sediments are frequently covered by ferruginous horizons.

(c)

Lower Pleistocene–Holocene Baucau Limestone (Baucau Formation)

It is predominantly composed of coral reef limestones along with a minor proportion of calcarenites, calcirudites, and conglomerates (submature graywackes). This formation is expected to provide evidence of the uplift of the island. This formation belongs to the Synorogenic Megasequence.

(d)

Pliocene Dilor Conglomerate (Dilor Formation)

This formation is part of the Synorogenic Megasequence and consists of conglomerates and sandstones with a significant contribution of detritus from the Lolotoi Complex, particularly quartzite.

(e)

Upper Miocene–Lower Pliocene Viqueque Formation (Synorogenic Viqueque Megasequence)

Lithologically, this formation is separated into lower (described as “more clayey and silty”) and upper (characterized as “more silty and sandy”) sections. Large amounts of silty marls, marly siltstones, silty claystones, siltstones, and sandstones, along with minor proportions of calcilutites and biocalcarenites are present in the upper section. The lower section is mostly composed of marls, clayey marls, silty marls, claystones, silty claystones, calcilutites, and tuffs, with minor amounts of basal conglomerates and mottled marls. These rocks are mostly formed by foraminifera fossils and skeletal radiolarians as well as rock fragments and mineral particles, which are associated with carbonate, metamorphic, volcanic, and other sedimentary rocks found in the Lolotoi Complex, Maubisse Formation, Aitutu Formation, Wailuli Formation, and Bobonaro Complex. This formation is included in the Synorogenic Megasequence.

(f)

Middle Miocene Bobonaro Complex (Bobonaro Formation or Bobonaro Scaly-Clay or Bobonaro Mélange or Synorogenic Mélange)

This unit is part of the Synorogenic Mélange and is primarily composed of exotic blocks within a scaly clay matrix. The matrix lithology is similar to that of mudstone of the Wailuli Formation. Exotic blocks of Permian to Cretaceous ages are common and widely distributed, although absent in several areas.

(g)

Oligocene–Miocene Cablac Limestone (Cablac Formation)

This formation is largely composed of oolitic and peloidal limestones and pelagic carbonates with small amounts of intraformational conglomerates, calcilutites, calcarenites, agglomerates, and tuffaceous rocks. The most common clasts of conglomerates are volcanic rocks, calcilutites containing foraminifera, radiolarian chert, biomicarenites, and detrital minerals, such as quartz and magnetite. Several rocks have been affected by alteration processes such as dolomitization and a few have undergone partial silicification, desilicification, and dedolomitization. This formation belongs to the Banda Terrane unit.

(h)

Oligocene Barique Formation

This formation belongs to the Banda Terrane unit and is largely composed of mafic to acidic lavas and tuffs, with minor amounts of serpentinites, volcanic conglomerates, and sandstones. Pillow lava is also observed. Significant alterations are observed in most volcanic rocks. Volcanic rocks are considered to have formed at mid-oceanic ridges and volcanic arcs.

(i)

Middle–Upper Eocene Dartollu Limestone (Dartolu Formation)

This limestone is part of the Banda Terrane unit and its primary constituents are algal and alveolina biomicarenites with minor proportions of calcilutites, siliceous shales, and siltstones. Dolomitization or silicification was not observed.

(j)

Lower–Upper Cretaceous Waibua Formation

This formation is part of the Australian-Margin Megasequence and is largely composed of radiolarites, radiolarian cherts, marls, and shales, with several percentages of calcilutites, marls, and calcarenites. Radiolaria and pelagic foraminifera are important components of these rocks and most limestones are completely or partially silicified. Radiolarian shales, marls, and radiolarites often occur in association with Mn nodules and ferromanganiferous rocks. The formation processes of radiolarites and cherts are closely associated with Mn-rich strata.

(k)

Late Triassic–Middle Jurassic Wailuli Formation

This formation predominantly consists of gray shales and blue-gray marls with minor amounts of sandstones, mudstones, quartz-arenites, coarse polymictic conglomerates, calcarenites, and calcilutites. Most shales are composed of fine micaceous minerals and microcrystalline carbonates. In some areas, small amounts of pyrite are present in the shales, whereas salt pseudomorphs and gypsum are present in gypsiferous shales, calcilutites, calcarenites, and quartz-arenites. Quartz-arenites contain considerable amounts of mica, and radiolarian and foraminiferal tests are the primary constituents of the calcilutites. This formation is a part of the Gondwana Megasequence.

(l)

Middle–Upper Triassic Aitutu Formation

This formation consists mostly of calcilutites, shales, and calcareous shales with minor amounts of marls, calcarenites, lumachelles, quartz-arenites, radiolarites, bituminous rocks, and chert. Radiolarian fossils are significant components of limestones but are partly or almost entirely filled with sparry calcite. Several limestones have been affected by alteration processes such as silicification, dedolomitization, and pyritization. This formation belongs to the Gondwana Megasequence.

(m)

Triassic–Late Cretaceous Lolotoi Complex (Lolotoi Formation or Lolotoi Metamorphic Complex)

Belonging to the Banda Terrane units, this complex is composed of regionally metamorphosed sedimentary and volcanic rocks, as well as basic and ultrabasic volcanic rocks. These include greenschists, graphitic phyllites, quartz mica schists, amphibolite gneisses and schists, garnet-bearing pelitic gneisses and schists, metagabbros, granulites, garnet mica schists, mafic and felsic igneous, pelitic schists, metabasite schists, carbonate-rich greenschists, peridotites, blueschists, serpentinites, and pyroxenites. The metamorphic rocks of the Lolotoi Complex mostly originate from sedimentary rocks and some metavolcanic rocks have undergone considerable alteration. The forearc region is thought to have been the location of the deposition of sedimentary rocks, and the rock components are thought to have originated from intermediate to mafic continental and oceanic arcs. Volcanic rocks were formed at volcanic arcs and mid-oceanic ridges.

(n)

Permian–Triassic Maubisse Formation (Maubisse Limestone)

This formation belongs to the Gondwana Megasequence and is mainly composed of fossiliferous limestones and volcanic rocks, as well as other types of sedimentary rocks. These include well-bedded dense biocalcarenites, massive reef limestones, pink crinoidal limestones, calcirudites, sandstones, calcareous shales, micaceous siltstones, tuffs, volcanic conglomerates, basalts, marbles, and metamorphosed basic volcanics. The basalts are pillowed and amygdaloidal and have an alkaline chemical composition. Alteration processes have affected most rocks of the Maubisse Formation, and limestones have been partially affected by alteration processes such as silicification, dolomitization, and chloritization.

3. Sampling and Analytical Methods

3.1. Sampling Method

The sampling and sample preparation procedures were implemented in this study according to the general methodology described by Fletcher [32], Yamamoto et al. [40], Darnley et al. [80], Hale and Plant [81], Ohta et al. [82], and Tanaka et al. [83]. A total of 53 modern river sand samples were collected during the dry season from ten permanent rivers or catchment areas (i.e., the Aiasa, Turon, Ermeti, Holarua, Karau Ulun, Soin, Merek, Laclo do Sul, Clerec, and Sahe Rivers) (Figure 1C). Coordinates and other field-related information, such as geology, geomorphology, and land use, were documented at each sampling point. To avoid sampling errors and heterogeneity of the analytical results, approximately 4 kg of four subsamples were collected over a distance of 20 m at each sampling point. Access conditions, topographic relief, and availability time influenced the sampling point distribution (Figure 2).

River sand samples were transported to the laboratory under wet conditions for preparation and chemical analysis. To obtain grain-size fractions of 180–150 μm and <150 μm, the samples were dried in an oven at 105 °C and then sieved using a vibrating sieve shaker machine. Manual crushing using an agate mortar and pestle was followed by machine crushing using a disk mill. Subsequently, the organic matter and volatile substances were removed using the loss-on-ignition method, which was verified by weighing the weight loss after heating at 950 °C.

3.2. Analytical Method

According to Yamamoto and Morishita [84], glass beads are commonly used for sample preparation in XRF spectrometry analysis. Typically, glass beads are prepared by mixing a flux with a powdered sample.

Glass beads were prepared by fusing mixtures of powdered samples and alkali flux at a weight ratio of 1:10. An 8:2 mixture of lithium tetraborate (Li₂B₄O₇) and lithium metaborate (LiBO₂) was used as the alkali flux. The mixture was processed to prepare glass beads using a bead sampler machine (TK-4100 model, Amena Tech Co., Yokohama, Japan) after placing the mixed powder in a platinum crucible. At the Division of Instrumental Analysis, Gifu University, modern river sand samples were examined by wavelength-dispersive X-ray fluorescence (WDXRF). Ten major elements (SiO₂, TiO₂, Fe₂O₃, Al₂O₃, MnO, MgO, Na₂O, K₂O, P₂O₅, and CaO) were determined and reference samples of igneous and sedimentary rocks provided by the Geological Survey of Japan were used for calibration.

3.3. Statistical Analysis

The major element compositions to be statistically analyzed and discussed were normalized based on the estimated average concentration of elements in the Upper Continental Crust (UCC) [85] and Post-Archean Australian Shale (PAAS) [45] (

Table 1. WDXRF geochemical results of modern river sands from the study area, including some selected ratios, ICV, and descriptive statistics of average and standard deviation for each basin. Post-Archean Australian Shales (PAAS) [45] and upper continental crust (UCC) [85] values are also presented for comparison.

Catchment Area	Sample Code	Weight % (wt%)
		SiO2	TiO2	Al2O3	Fe2O3	MnO	MgO	CaO
Aiasa River	SS01	51.65	1.32	17.60	9.32	0.21	3.67	5.58
	SS02	50.78	1.13	16.30	7.98	0.18	3.38	8.84
	SS017	50.61	1.05	15.40	7.88	0.17	3.26	9.48
	SS018	50.74	1.03	15.30	7.33	0.19	3.15	10.47
	SS032	51.74	0.92	14.10	6.53	0.17	3.12	10.83
	Avg.	51.10	1.09	15.74	7.81	0.18	3.32	9.04
	Std.	0.54	0.15	1.30	1.02	0.02	0.22	2.09
Turon River	SS029	39.00	0.67	10.40	4.75	0.09	2.11	24.25
	SS030	47.30	0.88	12.30	5.91	0.15	2.63	16.19
	Avg.	43.15	0.78	11.35	5.33	0.12	2.37	20.22
	Std.	5.87	0.15	1.34	0.82	0.04	0.37	5.70
Ermeti River	SS010	55.01	1.08	15.70	8.40	0.14	3.99	6.99
	SS011	47.70	1.14	12.90	7.54	0.18	3.84	14.22
	Avg.	51.36	1.11	14.30	7.97	0.16	3.92	10.61
	Std.	5.17	0.04	1.98	0.61	0.03	0.11	5.11
Holarua River	SS03	47.92	1.20	13.80	8.19	0.16	3.03	13.43
	SS04	36.84	1.11	11.00	8.22	0.14	3.12	23.21
	SS06	44.69	1.00	11.80	7.49	0.11	2.27	17.70
	Avg.	43.15	1.10	12.20	7.97	0.14	2.81	18.11
	Std.	5.70	0.10	1.44	0.41	0.03	0.47	4.90
Karau Ulun River	SS05	51.79	1.25	13.60	8.82	0.17	3.01	10.71
	SS07	50.77	1.25	15.50	8.76	0.18	3.43	9.86
	SS08	53.59	1.16	14.60	8.94	0.17	3.15	9.56
	SS09	55.50	1.13	12.30	6.61	0.24	2.47	10.00
	SS024	45.52	1.08	12.40	7.30	0.17	3.09	15.99
	SS026	47.29	1.11	12.90	7.80	0.16	3.11	13.83
	SS027	49.50	1.21	13.40	8.45	0.17	3.08	12.32
	SS028	49.00	1.15	13.50	8.17	0.15	2.98	12.47
	SS031	52.88	1.05	13.20	6.41	0.16	2.66	12.60
	Avg.	50.65	1.15	13.49	7.92	0.17	3.00	11.93
	Std.	3.16	0.07	1.02	0.96	0.02	0.28	2.12
Soin River	SS019	48.53	1.52	13.80	10.79	0.23	3.14	10.84
	SS020	52.72	1.48	15.40	9.36	0.24	3.29	8.43
	SS021	44.86	1.37	13.20	10.07	0.26	3.02	13.31
	SS022	52.47	1.60	16.40	9.94	0.17	3.56	6.98
	SS023	52.82	1.71	16.60	11.54	0.18	3.61	6.04
	SS025	47.69	1.48	13.40	9.13	0.25	3.22	13.01
	SS033	52.87	1.20	13.30	7.55	0.22	2.98	11.31
	SS036	52.30	1.18	13.20	7.52	0.23	2.97	11.10
	SS037	52.35	1.37	13.50	8.77	0.24	3.10	10.28
	SS038	54.53	1.00	13.60	6.69	0.21	2.88	11.05
	Avg.	51.11	1.39	14.24	9.13	0.22	3.18	10.24
	Std.	3.03	0.21	1.35	1.54	0.03	0.25	2.39
Laclo do Sul River	SS040	55.81	1.20	17.90	9.28	0.17	4.32	4.93
	SS041	54.09	1.25	17.60	9.50	0.18	4.41	5.15
	SS042	54.66	1.25	17.60	9.29	0.16	4.33	5.18
	SS044	54.23	1.23	17.20	9.21	0.18	4.40	6.59
	SS045	50.13	1.50	17.10	11.73	0.19	4.70	7.94
	SS046	54.53	1.19	16.80	9.26	0.18	4.30	6.85
	SS047	55.33	1.14	16.40	8.57	0.17	4.39	6.86
	Avg.	54.11	1.25	17.23	9.55	0.18	4.41	6.21
	Std.	1.86	0.12	0.52	1.00	0.01	0.14	1.14
Catchment Area	Sample Code	Weight % (wt%)			Ratios			ICV
		Na2O	K2O	P2O5	SiO2/ Al2O3	K2O/ Na2O	Na2O/ TiO2
Aiasa River	SS01	2.17	2.15	0.26	2.93	0.99	1.64	1.18
	SS02	2.00	2.08	0.23	3.12	1.04	1.78	1.14
	SS017	2.04	1.97	0.21	3.29	0.97	1.95	1.18
	SS018	2.06	1.86	0.21	3.32	0.90	1.99	1.14
	SS032	2.06	1.64	0.20	3.67	0.80	2.24	1.16
	Avg.	2.07	1.94	0.22	3.26	0.94	1.92	1.16
	Std.	0.06	0.20	0.02	0.27	0.09	0.23	0.02
Turon River	SS029	1.57	0.99	0.15	3.75	0.63	2.34	1.12
	SS030	1.96	1.36	0.18	3.85	0.69	2.22	1.19
	Avg.	1.77	1.17	0.17	3.80	0.66	2.28	1.15
	Std.	0.28	0.27	0.02	0.07	0.05	0.08	0.05
Ermeti River	SS010	2.09	1.34	0.15	3.50	0.64	1.93	1.21
	SS011	1.95	1.03	0.18	3.70	0.53	1.72	1.35
	Avg.	2.02	1.19	0.16	3.60	0.58	1.82	1.28
	Std.	0.10	0.22	0.02	0.14	0.08	0.15	0.10
Holarua River	SS03	2.17	1.28	0.21	3.47	0.59	1.81	1.30
	SS04	1.64	0.68	0.16	3.35	0.41	1.48	1.49
	SS06	1.26	1.09	0.16	3.79	0.86	1.26	1.22
	Avg.	1.69	1.01	0.18	3.54	0.62	1.51	1.34
	Std.	0.46	0.31	0.03	0.23	0.23	0.28	0.14
Karau Ulun River	SS05	1.81	1.33	0.20	3.81	0.73	1.45	1.32
	SS07	2.11	1.53	0.22	3.28	0.72	1.68	1.24
	SS08	2.06	1.45	0.21	3.67	0.70	1.77	1.29
	SS09	1.06	1.84	0.23	4.51	1.74	0.94	1.16
	SS024	1.80	1.16	0.20	3.67	0.65	1.67	1.31
	SS026	1.72	1.29	0.19	3.67	0.75	1.55	1.30
	SS027	1.69	1.42	0.22	3.69	0.84	1.40	1.31
	SS028	1.70	1.45	0.21	3.63	0.86	1.48	1.27
	SS031	2.47	1.17	0.18	4.01	0.47	2.35	1.22
	Avg.	1.82	1.40	0.21	3.77	0.83	1.59	1.27
	Std.	0.38	0.21	0.02	0.34	0.36	0.37	0.05
Soin River	SS019	2.22	1.39	0.23	3.52	0.63	1.46	1.54
	SS020	2.54	1.51	0.23	3.42	0.59	1.72	1.34
	SS021	1.81	1.39	0.22	3.40	0.77	1.32	1.48
	SS022	2.57	1.64	0.24	3.20	0.64	1.61	1.33
	SS023	2.59	1.60	0.27	3.18	0.62	1.52	1.42
	SS025	2.13	1.27	0.23	3.56	0.60	1.44	1.45
	SS033	2.24	1.32	0.20	3.98	0.59	1.87	1.32
	SS036	2.17	1.30	0.20	3.96	0.60	1.84	1.31
	SS037	2.12	1.28	0.20	3.88	0.61	1.54	1.39
	SS038	2.26	1.39	0.20	4.01	0.62	2.25	1.21
	Avg.	2.27	1.41	0.22	3.61	0.62	1.66	1.38
	Std.	0.24	0.13	0.02	0.32	0.05	0.27	0.10
Laclo do Sul River	SS040	2.74	1.64	0.23	3.12	0.60	2.29	1.22
	SS041	2.62	1.48	0.25	3.07	0.57	2.10	1.24
	SS042	2.68	1.52	0.25	3.11	0.57	2.14	1.23
	SS044	2.54	1.24	0.22	3.15	0.49	2.07	1.23
	SS045	2.28	1.10	0.22	2.93	0.48	1.52	1.38
	SS046	2.57	1.40	0.22	3.25	0.54	2.16	1.26
	SS047	2.72	1.21	0.20	3.37	0.45	2.40	1.26
	Avg.	2.59	1.37	0.23	3.14	0.53	2.10	1.26
	Std.	0.16	0.19	0.02	0.14	0.06	0.28	0.05
Catchment Area	Sample Code	Weight % (wt%)
		SiO2	TiO2	Al2O3	Fe2O3	MnO	MgO	CaO
Merek River	SS039	53.33	0.78	14.40	6.17	0.19	2.40	10.70
	SS043	58.19	0.94	15.40	7.53	0.26	2.48	6.68
	Avg.	55.76	0.86	14.90	6.85	0.22	2.44	8.69
	Std.	3.44	0.11	0.71	0.96	0.05	0.06	2.84
Clerec River	SS035	56.32	1.48	15.70	8.82	0.23	3.53	6.86
	SS048	52.79	1.54	17.00	9.85	0.25	4.41	6.58
	SS049	59.94	0.76	13.10	5.87	0.32	1.66	8.17
	SS050	52.31	2.17	15.70	11.94	0.29	4.05	6.99
	SS051	56.96	1.35	16.10	8.46	0.19	3.86	5.80
	SS052	57.58	1.34	16.90	8.51	0.19	3.90	5.86
	SS053	57.71	1.06	14.90	7.55	0.20	3.37	6.57
	Avg.	56.23	1.38	15.63	8.72	0.24	3.54	6.69
	Std.	2.75	0.44	1.33	1.88	0.05	0.90	0.80
Sahe River	SS012	56.85	0.78	14.80	6.11	0.14	2.02	8.20
	SS013	52.80	1.49	13.50	7.51	0.26	2.23	11.23
	SS014	52.50	0.83	13.20	5.99	0.16	2.10	12.05
	SS015	38.30	1.44	9.97	6.59	0.25	1.86	23.49
	SS016	49.74	1.32	13.20	6.81	0.24	2.41	13.76
	SS034	57.20	1.42	13.80	7.10	0.23	2.33	9.40
	Avg.	51.23	1.21	13.08	6.68	0.21	2.16	13.02
	Std.	6.94	0.32	1.63	0.58	0.05	0.20	5.49
-	UCC	66.62	0.64	15.40	5.04	0.10	2.48	3.59
-	PAAS	62.80	1.00	18.90	6.50	0.11	2.20	1.30
Catchment Area	Sample Code	Weight % (wt%)			Ratios			ICV
		Na2O	K2O	P2O5	SiO2/ Al2O3	K2O/ Na2O	Na2O/ TiO2
Merek River	SS039	1.92	1.78	0.19	3.70	0.93	2.47	1.04
	SS043	2.26	1.70	0.21	3.78	0.75	2.41	1.12
	Avg.	2.09	1.74	0.20	3.74	0.84	2.44	1.08
	Std.	0.24	0.06	0.01	0.05	0.12	0.04	0.05
Clerec River	SS035	2.45	1.41	0.19	3.59	0.57	1.66	1.28
	SS048	2.24	1.63	0.21	3.11	0.73	1.45	1.29
	SS049	1.46	1.88	0.17	4.58	1.29	1.93	1.01
	SS050	2.48	1.24	0.20	3.33	0.50	1.14	1.55
	SS051	2.73	1.38	0.21	3.54	0.50	2.03	1.27
	SS052	2.79	1.42	0.20	3.41	0.51	2.08	1.22
	SS053	2.46	1.46	0.18	3.87	0.59	2.33	1.23
	Avg.	2.37	1.49	0.19	3.63	0.67	1.80	1.27
	Std.	0.44	0.21	0.01	0.48	0.28	0.41	0.16
Sahe River	SS012	1.38	2.09	0.15	3.84	1.51	1.77	0.93
	SS013	1.69	1.54	0.18	3.91	0.91	1.13	1.20
	SS014	1.62	1.73	0.17	3.98	1.06	1.94	1.05
	SS015	1.13	1.16	0.16	3.84	1.03	0.79	1.35
	SS016	1.92	1.27	0.17	3.77	0.66	1.46	1.19
	SS034	2.11	1.40	0.19	4.14	0.66	1.49	1.20
	Avg.	1.64	1.53	0.17	3.91	0.97	1.43	1.15
	Std.	0.35	0.34	0.01	0.13	0.32	0.42	0.14
-	UCC	3.27	2.80	0.15	4.33	0.86	5.11	1.16
-	PAAS	1.20	3.70	0.16	3.32	3.08	1.20	0.85

ICV = index of compositional variability; Avg. = average; and Std. = standard deviation.

).

In order to identify the enrichment or abundance of major elements in the river sand samples from the study area, the “enrichment factors” (EF) were calculated [86,87,88,89]. Enrichment factors (EF) are calculated by comparing the concentrations of major elements in river sand samples with the average concentrations of Post-Archean Australian Shale (PAAS) [45]. The following formula is used to determine these factors: XEF = [(X/Al)SAMPLE/(X/Al)PAAS], where X represents the element in question, and Al represents aluminum, with both expressed as their respective weight concentration values.

In this study, several ratios of selected major elements, the Pearson correlation coefficient matrix, and the index of compositional variability (ICV) were used to analyze and interpret provenance [50,51,52,53,90,91,92,93,94]. The ICV was calculated as weight percent (wt%) proportions (ICV = $[{\mathrm{Fe}}_2{\mathrm{O}}_3+{\mathrm{K}}_2\mathrm{O}+{\mathrm{Na}}_2\mathrm{O}+{\mathrm{CaO}}^{*}+\mathrm{MgO}+\mathrm{MnO}+{\mathrm{TiO}}_2]/{\mathrm{Al}}_2{\mathrm{O}}_3$) [95]. To avoid mistakes in the analysis and interpretation of ICV values due to carbonate materials, which are abundant in the majority of sediments and sedimentary rocks [96], as well as the carbonate rocks that contribute to the CaO enrichment in river sand samples, the CaO* value represents Ca, which is only present in silicate minerals. According to the concept that the molecular CaO/Na₂O ratio of silicate is not greater than one, the CaO* value is considered to be equivalent to the Na₂O content [46,78].

To simplify and evaluate the results of the geochemical analysis by reducing the dimensionality of the datasets, exploring elemental associations, and allowing the interpretation of variance within the dataset based on major controlling factors, a multivariate statistical technique, principal component analysis (PCA) [97], was used. To analyze and interpret PCA results in a biplot of joint graphical representations of variables and samples, only principal components with eigenvalues greater than or near 1.0 were used because they explain the majority of the variance in the data [98,99].

Chemical and statistical analyses were performed using Microsoft Office Excel version 2405 (Build 17628.20144) and JMP Pro 14.0. The maps presented in this work were created using ArcGIS 10.4.

4. Analytical Results

4.1. Geochemical Features of River Sand Samples

The chemical analysis and statistical summary results of river sand samples from ten drainage basins in the study area are shown in (Table 1). The major elements of the river sand samples from the study area reveal considerable variations. The SiO₂, Al₂O₃, CaO, TiO₂, Fe₂O₃, MnO, MgO, Na₂O, K₂O, and P₂O₅ contents ranged from 36.84 to 59.94, 9.97 to 17.90, 4.93 to 24.25, 0.67 to 2.17, 4.75 to 11.94, 0.09 to 0.32, 1.66 to 4.70, 1.06 to 2.79, 0.68 to 2.15, and 0.15 to 0.27 wt%, respectively.

The highest concentrations of SiO₂, TiO₂, Fe₂O₃, MnO, and Na₂O were recorded in the Clerec River catchment, with average values of 56.23 wt% (ranging from 52.31 to 59.94 wt%), 1.38 wt% (ranging from 0.76 to 2.17 wt%), 8.72 wt% (ranging from 5.87 to 11.94 wt%), 0.24 wt% (ranging from 0.19 to 0.32 wt%), and 2.37 wt% (ranging from 1.46 to 2.79 wt%), respectively. The majority of these highest concentration values were observed near the midstream areas (also shown in Figure 3). In the Laclo do Sul River catchment, the highest concentrations of Al₂O₃ and MgO were reported (can also be seen in Figure 3), the measured average values were 17.23 wt% (ranging from 16.40 to 17.90 wt%) and 4.41 wt% (ranging from 4.30 to 4.70 wt%), respectively. The highest concentrations of K₂O and P₂O₅ were reported in the upstream areas of the Aiasa and Soin River catchments (see also Figure 3), with average values measured at 1.94 wt% (ranging from 1.64 to 2.15 wt%) and 0.22 wt% (ranging from 0.20 to 0.27 wt%), respectively. In addition, the concentrations of CaO in the Turon, Sahe, and Holarua River catchments were measured to be the highest, while the concentrations of all other major elements were low (see also Figure 3). In these catchment regions, the average CaO concentrations were measured to be 20.22 wt% (ranging from 16.19 to 24.25 wt%), 13.02 wt% (ranging from 8.20 to 23.49 wt%), and 18.11 wt% (ranging from 13.43 to 23.21 wt%), respectively.

4.2. Comparison with UCC and PAAS

The results of the UCC- and PAAS-normalized patterns for the major elements of the river sand samples from the study area are shown in Figure 4. The bulk composition of the UCC is granodioritic and representative of the continental crust [85]. In contrast, PAAS represents a crustal shale sedimentary rock bulk composition [45].

In comparison with the average major element compositions of the UCC and PAAS (Figure 4A,B), the composition of the river sand samples from the ten drainage basins revealed a significant depletion in K₂O, a slight depletion in SiO₂, a slight depletion to considerable enrichment in MgO, a slight enrichment in P₂O₅, slight to considerable enrichments in TiO₂, Fe₂O₃, and MnO, and considerable to significant enrichments in CaO. However, Turon and Holarua had more abundance and Laclo do Sul and Clerec had lower abundance than in the other river catchments. The UCC-normalized patterns (Figure 4A) showed considerable depletion of Na₂O, and the concentration of Al₂O₃ was enriched in the Aiasa, Laclo do Sul, and Clerec drainage basins and depleted in the other river catchments. In contrast, compared to the average composition of the PAAS (Figure 4B), Na₂O was enriched and Al₂O₃ was depleted.

5. Discussion

The results of the bulk geochemical composition analysis of the river sand samples from the study area showed an abundance of CaO, a slight depletion in SiO₂ and Al₂O₃ contents, as well as depletion of K₂O, and variations in Na₂O concentrations. These findings suggested that geochemical composition of the river sands from study area were mostly controlled by the destruction of carbonate, clay and plagioclase minerals, which were related to the major contributions from the carbonate sedimentary rocks of the northern edge of the Australian continental shelf and from carbonate components that are integrated into clastic sedimentary rocks in different proportions [96,100,101].

5.1. The Enrichment of the Elements

River sand samples were collected from the ten drainage basins in the study area, which are dominated by fine to coarse sand fractions. In order to evaluate elemental mobility during weathering and transportation, the average concentrations of major elements in the analyzed samples were compared to the mean compositions of a sandstone reported by Turekian and Wedepohl [102]. The results of the comparison showed that SiO₂ was depleted, while other major elements were enriched.

The enrichment of Al₂O₃ concentration in river sand samples can be attributed to significant contributions from clay minerals, particularly those associated with fine-grained sedimentary rocks such as clay and silt [95,103,104]. The results of the Pearson correlation coefficient matrix for major elements (

Table 2. Pearson correlation coefficient between major elements and SiO₂/Al₂O₃ ratio in river sand samples from selected drainage basin within the study area. (A) Soin; (B) Laclo do Sul; (C) Clerec; and (D) Sahe. The positive correlations of SiO₂, Al₂O₃, and CaO with other major elements, as well as the positive correlation observed between TiO₂, Fe₂O₃, MgO, and other major elements, are denoted by boldface type. Emphasized values with shaded cells indicate the negative associations between TiO₂, MgO, Fe₂O₃, and P₂O₅ with the SiO₂/Al₂O₃ ratio.

(A)	SiO2	TiO2	Al2O3	Fe2O3	MnO	MgO	CaO	Na2O	K2O	P2O5	SiO2/ Al2O3
SiO2	1.00
TiO2	−0.26	1.00
Al2O3	0.36	0.71	1.00
Fe2O3	−0.43	0.93	0.59	1.00
MnO	−0.60	−0.32	−0.76	−0.20	1.00
MgO	0.10	0.90	0.92	0.75	−0.63	1.00
CaO	−0.60	−0.57	−0.94	−0.43	0.81	−0.81	1.00
Na2O	0.68	0.45	0.87	0.25	−0.78	0.73	−0.91	1.00
K2O	0.27	0.60	0.94	0.56	−0.74	0.80	−0.85	0.77	1.00
P2O5	−0.20	0.91	0.79	0.90	−0.43	0.88	−0.60	0.53	0.74	1.00
SiO2/ Al2O3	0.33	−0.90	−0.76	−0.89	0.33	−0.86	0.53	−0.41	−0.77	−0.94	1.00
(B)	SiO2	TiO2	Al2O3	Fe2O3	MnO	MgO	CaO	Na2O	K2O	P2O5	SiO2/ Al2O3
SiO2	1.00
TiO2	−0.96	1.00
Al2O3	0.11	0.14	1.00
Fe2O3	−0.95	0.99	0.12	1.00
MnO	−0.77	0.64	−0.31	0.69	1.00
MgO	−0.94	0.90	−0.15	0.90	0.77	1.00
CaO	−0.67	0.48	−0.76	0.51	0.77	0.66	1.00
Na2O	0.96	−0.89	0.18	−0.90	−0.86	−0.87	−0.75	1.00
K2O	0.66	−0.46	0.73	−0.44	−0.73	−0.71	−0.92	0.70	1.00
P2O5	0.15	0.04	0.87	−0.02	−0.45	−0.29	−0.80	0.23	0.74	1.00
SiO2/ Al2O3	0.71	−0.86	−0.61	−0.84	−0.39	−0.64	0.00	0.64	0.01	−0.49	1.00
(C)	SiO2	TiO2	Al2O3	Fe2O3	MnO	MgO	CaO	Na2O	K2O	P2O5	SiO2/ Al2O3
SiO2	1.00
TiO2	−0.90	1.00
Al2O3	−0.61	0.58	1.00
Fe2O3	−0.94	0.99	0.63	1.00
MnO	−0.11	0.05	−0.58	0.02	1.00
MgO	−0.78	0.74	0.94	0.79	−0.52	1.00
CaO	0.21	−0.28	−0.82	−0.32	0.91	−0.77	1.00
Na2O	−0.33	0.50	0.78	0.50	−0.82	0.80	−0.93	1.00
K2O	0.51	−0.76	−0.57	−0.73	0.49	−0.72	0.64	−0.87	1.00
P2O5	−0.65	0.66	0.91	0.70	−0.47	0.90	−0.79	0.75	−0.61	1.00
SiO2/ Al2O3	0.82	−0.78	−0.95	−0.83	0.41	−0.99	0.70	−0.73	0.66	−0.90	1.00
(D)	SiO2	TiO2	Al2O3	Fe2O3	MnO	MgO	CaO	Na2O	K2O	P2O5	SiO2/ Al2O3
SiO2	1.00
TiO2	−0.39	1.00
Al2O3	0.97	−0.46	1.00
Fe2O3	0.03	0.88	−0.03	1.00
MnO	−0.46	0.99	−0.51	0.86	1.00
MgO	0.53	0.30	0.52	0.52	0.29	1.00
CaO	−0.99	0.41	−0.99	−0.02	0.47	−0.53	1.00
Na2O	0.62	0.26	0.53	0.47	0.22	0.95	−0.58	1.00
K2O	0.67	−0.83	0.73	−0.51	−0.86	−0.19	−0.70	−0.15	1.00
P2O5	0.38	0.60	0.24	0.75	0.56	0.81	−0.33	0.89	−0.40	1.00
SiO2/ Al2O3	0.47	0.11	0.23	0.20	0.00	0.22	−0.38	0.52	0.03	0.61	1.00

) showed a positive correlation between most of the major elements and Al₂O₃ in most of the study area’s river basins. This suggests that clay minerals are also responsible for the distribution and enrichment of most major elements in the river sands from the study area. It is compatible with the results and conclusions of Hossain et al. [54], Biswas et al. [90], and Cai et al. [105].

The enrichment factor (EF) values have been established to evaluate the leaching and enrichment degrees of major elements in river sand samples. The values higher than 1 indicate enrichment, while values lower than 1 disclose depletion [88,89]. Moreover, enrichment may be detected with EF values more than 3, while moderate to significant enrichment is revealed by EF values greater than 10 [86,87]. The average calculations of the EF with respect to the mean concentrations of the PAAS (

Table 3. Statistical results of enrichment factor (EF) calculated with respect to average concentrations of the Post-Archean Australian Shale (PAAS) [45] for river sands from the study area.

Basins	Sample Code	SiEF	TiEF	FeEF	MnEF	MgEF	NaEF	KEF	PEF	CaEF
Aiasa	SS01	0.88	1.42	1.54	2.03	1.79	1.94	0.62	1.74	4.61
	SS02	0.94	1.31	1.42	1.86	1.78	1.93	0.65	1.67	7.88
	SS017	0.99	1.28	1.49	1.87	1.82	2.09	0.65	1.60	8.95
	SS018	1.00	1.28	1.39	2.10	1.77	2.12	0.62	1.61	9.95
	SS032	1.10	1.23	1.35	2.10	1.90	2.30	0.59	1.69	11.17
	Avg.	0.98	1.30	1.44	1.99	1.81	2.08	0.63	1.66	8.51
	Std	0.08	0.07	0.08	0.12	0.05	0.15	0.02	0.06	2.50
Turon	SS029	1.13	1.22	1.33	1.52	1.74	2.38	0.48	1.68	33.90
	SS030	1.16	1.35	1.40	2.10	1.84	2.51	0.56	1.75	19.14
	Avg.	1.14	1.29	1.36	1.81	1.79	2.44	0.52	1.71	26.52
	Std	0.02	0.10	0.05	0.40	0.07	0.09	0.06	0.05	10.44
Ermeti	SS010	1.05	1.30	1.56	1.56	2.18	2.10	0.44	1.11	6.47
	SS011	1.11	1.66	1.70	2.45	2.56	2.38	0.41	1.61	16.03
	Avg.	1.08	1.48	1.63	2.01	2.37	2.24	0.42	1.36	11.25
	Std	0.04	0.26	0.10	0.63	0.26	0.20	0.02	0.36	6.76
Holarua	SS03	1.05	1.64	1.73	2.02	1.89	2.48	0.47	1.81	14.15
	SS04	1.01	1.90	2.17	2.17	2.44	2.35	0.31	1.76	30.68
	SS06	1.14	1.61	1.85	1.57	1.65	1.68	0.47	1.63	21.81
	Avg.	1.06	1.72	1.91	1.92	1.99	2.17	0.42	1.73	22.21
	Std	0.07	0.16	0.23	0.31	0.40	0.43	0.09	0.09	8.27
Karau Ulun	SS05	1.15	1.74	1.88	2.17	1.90	2.10	0.50	1.72	11.45
	SS07	0.99	1.53	1.64	1.94	1.90	2.14	0.50	1.71	9.24
	SS08	1.10	1.50	1.78	1.94	1.85	2.22	0.51	1.68	9.52
	SS09	1.36	1.74	1.56	3.30	1.73	1.36	0.76	2.25	11.82
	SS024	1.10	1.64	1.71	2.30	2.14	2.29	0.48	1.92	18.75
	SS026	1.10	1.63	1.76	2.13	2.07	2.10	0.51	1.71	15.59
	SS027	1.11	1.70	1.83	2.22	1.97	1.99	0.54	1.90	13.37
	SS028	1.09	1.61	1.76	1.91	1.90	1.98	0.55	1.83	13.43
	SS031	1.21	1.51	1.41	2.12	1.73	2.95	0.45	1.61	13.88
	Avg.	1.13	1.62	1.70	2.23	1.91	2.12	0.53	1.81	13.00
	Std	0.10	0.09	0.15	0.42	0.14	0.41	0.09	0.19	2.98
Soin	SS019	1.06	2.09	2.27	2.84	1.95	2.53	0.51	1.99	11.42
	SS020	1.03	1.81	1.77	2.68	1.84	2.60	0.50	1.78	7.96
	SS021	1.02	1.96	2.22	3.41	1.97	2.16	0.54	2.00	14.66
	SS022	0.96	1.84	1.76	1.81	1.86	2.47	0.51	1.72	6.19
	SS023	0.96	1.94	2.02	1.86	1.87	2.46	0.49	1.89	5.29
	SS025	1.07	2.08	1.98	3.19	2.06	2.50	0.48	2.01	14.12
	SS033	1.20	1.70	1.65	2.86	1.92	2.65	0.51	1.78	12.36
	SS036	1.19	1.69	1.66	2.93	1.93	2.59	0.50	1.79	12.23
	SS037	1.17	1.92	1.89	3.09	1.97	2.47	0.49	1.76	11.07
	SS038	1.21	1.40	1.43	2.70	1.82	2.62	0.52	1.72	11.81
	Avg.	1.09	1.84	1.86	2.74	1.92	2.51	0.51	1.84	10.71
	Std	0.10	0.21	0.26	0.52	0.07	0.14	0.02	0.12	3.19
Laclo do Sul	SS040	0.94	1.26	1.51	1.65	2.07	2.41	0.47	1.54	4.00
	SS041	0.92	1.34	1.57	1.74	2.15	2.34	0.43	1.65	4.25
	SS042	0.93	1.34	1.53	1.58	2.11	2.40	0.44	1.64	4.28
	SS044	0.95	1.35	1.56	1.84	2.20	2.33	0.37	1.52	5.57
	SS045	0.88	1.66	1.99	1.95	2.36	2.10	0.33	1.49	6.75
	SS046	0.98	1.34	1.60	1.84	2.20	2.41	0.42	1.54	5.93
	SS047	1.02	1.31	1.52	1.82	2.30	2.61	0.38	1.43	6.08
	Avg.	0.95	1.37	1.61	1.77	2.20	2.37	0.41	1.54	5.27
	Std	0.04	0.13	0.17	0.13	0.10	0.15	0.05	0.08	1.08
Merek	SS039	1.11	1.02	1.25	2.21	1.43	2.10	0.63	1.58	10.80
	SS043	1.14	1.15	1.42	2.86	1.38	2.31	0.56	1.60	6.31
	Avg.	1.13	1.09	1.33	2.53	1.41	2.21	0.60	1.59	8.56
	Std	0.02	0.09	0.12	0.46	0.03	0.15	0.05	0.01	3.18
Clerec	SS035	1.08	1.78	1.63	2.56	1.93	2.46	0.46	1.41	6.35
	SS048	0.93	1.71	1.69	2.52	2.23	2.08	0.49	1.43	5.62
	SS049	1.38	1.09	1.30	4.18	1.09	1.76	0.73	1.53	9.06
	SS050	1.00	2.61	2.21	3.14	2.22	2.49	0.40	1.51	6.47
	SS051	1.06	1.58	1.53	1.97	2.06	2.67	0.44	1.53	5.24
	SS052	1.03	1.50	1.46	1.94	1.98	2.60	0.43	1.42	5.04
	SS053	1.17	1.34	1.47	2.25	1.94	2.60	0.50	1.44	6.41
	Avg.	1.09	1.66	1.61	2.65	1.92	2.38	0.49	1.47	6.31
	Std	0.14	0.48	0.29	0.79	0.39	0.34	0.11	0.05	1.34
Sahe	SS012	1.16	1.00	1.20	1.64	1.17	1.47	0.72	1.21	8.05
	SS013	1.18	2.09	1.62	3.32	1.42	1.97	0.58	1.56	12.09
	SS014	1.20	1.19	1.32	2.11	1.37	1.93	0.67	1.48	13.27
	SS015	1.16	2.72	1.92	4.31	1.60	1.79	0.59	1.85	34.25
	SS016	1.13	1.88	1.50	3.10	1.57	2.29	0.49	1.55	15.16
	SS034	1.25	1.94	1.50	2.89	1.45	2.41	0.52	1.60	9.90
	Avg.	1.18	1.80	1.51	2.89	1.43	1.98	0.60	1.54	15.45
	Std	0.04	0.63	0.25	0.94	0.15	0.34	0.09	0.21	9.54

Avg. = average; and Std. = standard deviation.

and Figure 5) indicated that CaO exhibited detectable to moderate enrichment, K₂O showed depletion, and TiO₂, Fe₂O₃, MnO, MgO, Na₂O, and P₂O₅ demonstrated enrichment across all drainage basins in the study area. In addition, SiO₂ displayed slight depletion in the Aiasa and Laclo do Sul catchment areas, while showed slight enrichment in the other river basins.

CaO, Na₂O, MgO and K₂O are widely known to be mobile major elements due to their mobility and leachability during weathering processes, and they are frequently depleted in river sands [106,107,108,109]. The lithology of the source rocks has a considerable influence on the enrichment of these major elements in the river sand samples from the study area.

SiO₂ exhibited high concentrations in the samples were collected in the areas drained from clastic sedimentary bedrock lithologies, which are associated with Wailuli, Viqueque, Ainaro and Suai Formations (Figure 3). The Na₂O/TiO₂ ratio (proposed by Yamamoto et al. [40]) values in the study area ranged from 0.79 to 2.47, with an average of 1.77, which is slightly higher than PAAS but lower than UCC (Table 1). The lowest Na₂O/TiO₂ ratio values, which were slightly lower than PAAS (less than 1.20), and the highest TiO₂ values were mostly recorded in samples drained from clastic sedimentary rock source areas affiliated with the Wailuli Formation (Figure 3). On the other hand, the highest Na₂O values were mostly observed in samples derived from metamorphic and igneous rocks affiliated with the Lolotoi Complex, Dilor Conglomerate, and Bobonaro Complex (as exotic blocks) that lie upstream. Additionally, the Pearson correlation coefficient matrix for most river basins of the study area showed that TiO₂ and Na₂O were positively correlated with SiO₂, Al₂O₃, Fe₂O₃, MnO, MgO, and P₂O₅. The enrichment of SiO₂ and TiO₂ in the study area could be attributed to significant contributions from quartz and clay minerals. The notable contributions from chlorite, biotite, amphibole, pyroxene, and garnet were likely responsible for the enrichment of Na₂O in the study area. These minerals also contribute to the abundance of TiO₂. These findings are consistent with the result and discussion of Yamamoto et al. [40] from a study of geochemical mapping in Aichi prefecture.

The results of the Pearson correlation for major elements (Table 2) showed a positive association between most major elements (particularly SiO₂ and Al₂O₃) and CaO in most of the study area’s drainage basins. Moreover, CaO revealed high concentrations in the samples mainly drained from carbonate sedimentary rock source areas, which are affiliated with Aitutu, Wailuli, and Viqueque Formations, as well as Dartollu Limestone (Figure 3). The abundance of CaO in the study area are possibly ascribed to the significant presence of carbonate minerals associated with carbonate and clastic sedimentary rocks in varying proportions. The highest concentrations of K₂O were mostly observed in the samples derived from clastic sedimentary bedrock source areas, particularly those associated with the Wailuli and Viqueque Formations (Figure 3). In most of the river basins in the study area, K₂O showed a positive association with SiO₂, Al₂O₃, and Na₂O, and a negative correlation with CaO and MnO (Table 2). These findings suggest that the distribution of K₂O in the study area may have been controlled by the destruction of feldspar, mica, and clay minerals.

The scattered areas of enrichment observed in the distribution patterns of Al₂O₃, Fe₂O₃, and MgO are quite similar to each other (Figure 3). Additionally, a positive relationship was observed between Al₂O₃, Fe₂O₃, and MgO in most of the study area’s drainage basins (Table 2). This suggests that these elements are mostly accumulated in finer grain sizes, like those of clay minerals. These findings are compatible with the results and discussion of Lim et al. [110] and von Eynatten et al. [111]. However, the distribution patterns of enrichment areas also showed some modest similarities between TiO₂, Fe₂O₃, MnO, P₂O₅, and MgO (Figure 3). These elements also exhibited positive correlations with one another across the majority of the drainage basins (Table 2). This suggests that the enrichment of these elements could be related to the contribution of mafic, heavy, and accessory minerals (e.g., amphibole, pyroxene, biotite, ilmenite, hematite, sphene, rutile, and garnet), which are mostly associated with igneous and metamorphic rocks. These findings are consistent with the results and discussions of Biswas et al. [90], Armstrong-Altrin [112], and Armstrong-Altrin et al. [113].

5.2. Geochemical Characteristics of the Drainage Basins

(1)

Aiasa River catchment

The Aiasa River catchment is covered by the Lolotoi and Bobonaro Complexes, as well as the Viqueque and Ainaro Formations (Figure 1C and Figure 3). This catchment area showed the highest concentrations of K₂O and P₂O₅, with average values of 1.94 wt% (ranging from 1.64 to 2.15 wt%) and 0.22 wt% (ranging from 0.20 to 0.26 wt%), respectively (Table 1). The highest values were registered in the area near the upstream (as shown in Figure 3). The concentrations of Al₂O₃, K₂O, TiO₂, Fe₂O₃, MgO, and P₂O₅ tended to decrease toward downstream, and on the contrary, CaO and Na₂O seemed to increase downstream. However, the high content value of Na₂O was recorded near the upstream area. The SiO₂ and MnO concentration values showed an irregular distribution pattern from upstream to downstream. The presence of CaO and Na₂O might be attributed to the presence of the calcite and halite minerals associated with carbonate components. Near the upstream area, Na₂O could be partly attributed to the existence of silicate and aluminosilicate minerals such as plagioclases, clays, and micas. Meanwhile, TiO₂, Fe₂O₃, MgO, K₂O, and P₂O₅ concentrations were mostly concentrated in clay minerals such as illite and others. In the upstream area, the composition of river sand is mostly controlled by clay contents and lithic fragments associated with clastic sedimentary rocks. On the other hand, carbonate components related to the carbonate sedimentary rocks make major contributions in the downstream region.

(2)

Turon River catchment

The highest content of CaO and the lowest concentrations of SiO₂, TiO₂, Al₂O₃, Fe₂O₃, MnO, K₂O, and P₂O₅ were reported in this river catchment (Table 1), which is mostly covered by the Viqueque and Ainaro Formations (Figure 1C and Figure 3). The average value of the highest concentration was measured to be 20.22 wt% (ranging from 16.19 to 24.25 wt%), and the lowest contents were 43.15 wt% (ranging from 39.00 to 47.30 wt%), 0.78 wt% (ranging from 0.67 to 0.88 wt%), 11.35 wt% (ranging from 10.40 to 12.30 wt%), 5.33 wt% (ranging from 4.75 to 5.91 wt%), 0.12 wt% (ranging from 0.09 to 0.15 wt%), 1.17 wt% (ranging from 0.99 to 1.36 wt%), and 0.17 wt% (ranging from 0.15 to 0.18 wt%), respectively (Table 1). The highest and lowest values were recorded in the midstream area (Figure 3). The abundance of CaO might be sourced from carbonate components, which contributed much more than others, while other major elements could be associated with clay and silicate minerals.

(3)

Ermeti River catchment

The Ermeti River catchment is mostly covered by the Ainaro Formation (Figure 1C and Figure 3). This catchment area showed high content of SiO₂ and low CaO, P₂O₅, and MnO concentrations, with average values of 51.36 wt% (ranging from 47.70 to 55.01 wt%), 10.61 wt% (ranging from 6.99 to 14.22 wt%), 0.16 wt% (ranging from 0.15 to 0.18 wt%), and 0.16 wt% (ranging from 0.14 to 0.18 wt%) (Table 1). SiO₂, Al₂O₃, Fe₂O₃, MgO, Na₂O, and K₂O contents appeared to increase in the upstream, while the concentrations of TiO₂, MnO, CaO, and P₂O₅ tended to decrease toward the downstream (Figure 3). TiO₂, MnO, CaO, and P₂O₅ could be attributed to the contribution of carbonate components along with manganese and apatite minerals, while clay and silicate minerals could be responsible for SiO₂, Al₂O₃, Fe₂O₃, MgO, Na₂O, and K₂O.

(4)

Holarua River catchment

The Holarua River catchment is covered by the Lolotoi Complex, Wailuli Formation, and Ainaro Formation (Figure 1C and Figure 3). This drainage basin also recorded the highest concentration of CaO and the lowest contents of SiO₂, Al₂O₃, MnO, Na₂O, and K₂O, with the average values reported at 18.11 wt% (ranging from 13.43 to 23.21 wt%), 43.15 wt% (ranging from 36.84 to 47.92 wt%), 12.20 wt% (range 11.00–13.80 wt%), 0.14 wt% (range 0.11–0.16 wt%), 1.69 wt% (range 1.26–2.17 wt%), and 1.01 wt% (range 0.68–1.28 wt%), respectively (Table 1). TiO₂, MnO, Na₂O, and P₂O₅ contents showed an increasing trend toward upstream, and SiO₂, K₂O, and Al₂O₃ concentrations appeared to increase toward downstream, but their high content values were observed close to the upstream area. Although the concentrations of CaO, Fe₂O₃, and MgO seemed to decrease toward downstream, their low measured values were found close to the upstream area (Figure 3). SiO₂, K₂O, and Al₂O₃ could be derived from the destruction of feldspar and/or muscovite minerals. TiO₂, MnO, Na₂O, and P₂O₅ were mostly accumulated in clay minerals, and these elements can be partly attributed to the presence of silicate and accessory minerals. The abundance of CaO, Fe₂O₃, and MgO could be sourced from calcite, dolomite, and pyrite minerals associated with carbonate components. The upstream and downstream areas are mostly influenced by clay and mica contents, as well as lithic fragments affiliated with clastic sedimentary rocks, which contribute to the composition of river sands. However, there were contributions from silicate and accessory minerals associated with metamorphic rocks in the upstream area. The midstream region is characterized by significant contributions from carbonate components, particularly those associated with carbonate sedimentary rocks.

(5)

Karau Ulun River catchment

This river catchment is mostly covered by the Lolotoi Complex, Wailuli Formation, Dartollu Limestone, Viqueque Formation, Dilor Conglomerate, and Ainaro Formation (Figure 1C and Figure 3). The lowest concentration of Na₂O was registered in this catchment area, with an average value of 1.82 wt% (range 1.06–2.47 wt%) (Table 1). The concentration values of CaO almost showed a decreasing trend toward downstream, and Al₂O₃ contents also nearly appeared to be increasing in the upstream direction. Near the upstream region, mostly high values of SiO₂, TiO₂, Fe₂O₃, MnO, MgO, Na₂O, K₂O, and P₂O₅ concentrations were recorded. A high content of CaO and low concentrations of TiO₂, Al₂O₃, K₂O, P₂O₅, Fe₂O₃, MnO, and Na₂O were reported in the downstream region. However, low Al₂O₃ content and high concentration values of SiO₂, K₂O, MnO, P₂O₅, and MgO were recorded in the sampling location SS09 (Figure 3). The significant contribution of clay, mica, silicate, and accessory minerals, as well as lithic fragments associated with clastic sedimentary and metamorphic rocks in the upstream region. In the downstream area, carbonate components associated with carbonate sedimentary rocks have important contributions. On the other hand, sample location SS09 is characterized by notable inputs from the silicate and accessory minerals, such as quartz, feldspar, muscovite, garnet, apatite, and chlorite, which are associated with metamorphic rocks.

(6)

Soin River catchment

This catchment area is covered by the Lolotoi Complex, Wailuli Formation, Bobonaro Complex, Viqueque Formation, Dilor Conglomerate, and Ainaro Formation (Figure 1C and Figure 3). The highest P₂O₅ content was recorded in this drainage basin, with the average value reported at 0.22 wt% (ranging from 0.20 to 0.27 wt%) (Table 1). As shown in Table 2A, SiO₂ showed a positive correlation with Al₂O₃, MgO, Na₂O, and K₂O, as opposed to Al₂O₃, which was negatively associated with MnO and CaO and positively correlated with all other major elements. CaO had a strong positive association with MnO and a negative relationship with all other elements. Positive relationships were observed between TiO₂, Fe₂O₃, MgO, Na₂O, K₂O, and P₂O₅. High amounts of TiO₂, Al₂O₃, MgO, Na₂O, K₂O, P₂O₅, Fe₂O₃, and SiO₂, along with low concentrations of CaO and MnO, were mostly recorded near the upstream areas (Figure 3). The midstream regions had low SiO₂ content and high concentrations of CaO, MnO, and Fe₂O₃. In addition, the downstream regions had high SiO₂, CaO, and MnO concentrations, and low content values of P₂O₅, MgO, TiO₂, Fe₂O₃, and Al₂O₃. The upstream areas could be influenced by clay and mica content as well as quartz, plagioclase, amphibole, chlorite, hematite, ilmenite, rutile, garnet, sphene, and apatite minerals, which are associated with clastic sedimentary and metamorphic rocks. Carbonate components and Mn minerals affiliated with carbonate sedimentary rocks, along with the clay content associated with clastic sedimentary rocks (e.g., shales and mudstones), made major contributions to the midstream regions. The downstream regions were mostly controlled by silicate minerals, such as quartz associated with clastic sedimentary rocks; carbonate components and manganese minerals affiliated with carbonate sedimentary rocks; along with clay content related to clastic sedimentary rocks.

(7)

Laclo do Sul River catchment

The Laclo do Sul River catchment is covered by the Lolotoi Complex, Wailuli Formation, and Bobonaro Complex, as well as the Viqueque, Ainaro, and Suai Formations (Figure 1C and Figure 3). The lowest content of CaO and highest values of Al₂O₃, MgO, Fe₂O₃, Na₂O, and P₂O₅ were registered near the upstream and downstream areas (Figure 3). The average values of the lowest and highest concentrations were measured to be 6.21 wt% (ranging from 4.93 to 7.94 wt%), 17.23 wt% (ranging from 16.40 to 17.90 wt%), 4.41 wt% (ranging from 4.30 to 4.70 wt%), 9.55 wt% (ranging from 8.57 to 11.73 wt%), 2.59 wt% (ranging from 2.28 to 2.74 wt%), and 0.23 wt% (ranging from 0.20 to 0.25 wt%), respectively (Table 1). As shown in Table 2B, SiO₂ was positively correlated with Na₂O, K₂O, P₂O₅, and Al₂O₃. Al₂O₃ was positively associated with SiO₂, TiO₂, Fe₂O₃, Na₂O, K₂O, and P₂O₅. Moderate-to-very strong correlations were observed between TiO₂, Fe₂O₃, MnO, MgO, and CaO. The Al₂O₃ concentration appeared to increase in the upstream direction. High SiO₂, Al₂O₃, K₂O, P₂O₅, Na₂O, TiO₂, Fe₂O₃, and MgO contents and low CaO and MnO concentrations were recorded near the upstream areas. Downstream and midstream regions, specifically sample location SS045, had high concentrations of Fe₂O₃, MgO, TiO₂, and MnO and low Na₂O and K₂O contents. In addition, high values of SiO₂, Na₂O, and CaO, along with low concentrations of TiO₂, Fe₂O₃, and Al₂O₃, were also observed in the downstream area (Figure 3). The destruction of clay and mica, along with quartz, plagioclase, amphibole, chlorite, hematite, ilmenite, rutile, garnet, sphene, and apatite minerals associated with clastic sedimentary and metamorphic rocks, contributed significantly to the composition of the river sands near the upstream regions. Near the downstream and continuing to the midstream regions, quartz and clay contents affiliated with clastic sedimentary rocks (e.g., shales and mudstones) made major contributions; however, in the sampling location SS045, there was significant inputs from mafic and heavy minerals related to the presence of igneous and metamorphic rocks that associated with the Bobonaro Complex, as exotic blocks that were incorporated into the clastic sedimentary rocks (such as shales and mudstones) [9,13,76]. Silicate minerals and clay related to clastic sedimentary rocks contributed significantly to the downstream area.

(8)

Merek River catchment

The Merek River catchment is mostly covered by the Wailuli Formation and Lolotoi Complex (Figure 1C and Figure 3). The highest and lowest concentrations of SiO₂ and TiO₂ were also recorded in this river catchment, with the average values reported at 55.76 wt% (ranging from 53.33 to 58.19 wt%) and 0.86 wt% (ranging from 0.78 to 0.94 wt%), respectively (Table 1). CaO and K₂O appeared to increase toward downstream, while the other major element contents showed an decreasing trend toward downstream (Figure 3). Silicate (such as quartz, plagioclase, amphibole, and pyroxene), and clay minerals might significantly contribute to the geochemical composition of the river sand samples from this river catchment. The remaining contributions could be attributed to the presence of carbonate components.

(9)

Clerec River catchment

The Clerec River catchment was registered as having the highest concentrations of SiO₂, TiO₂, Fe₂O₃, MnO, Na₂O, and MgO (Table 1). This catchment area is mostly covered by the Lolotoi and Bobonaro Complexes, as well as the Aitutu, Wailuli, Viqueque, and Suai Formations (Figure 1C and Figure 3). As demonstrated by the Pearson correlation of the Clerec River catchment (Table 2C), SiO₂ showed a positive association with CaO and K₂O, Al₂O₃ had a positive correlation with TiO₂, Fe₂O₃, Na₂O, P₂O₅, and MgO, and CaO showed a positive correlation with SiO₂, MnO, and K₂O. There was a moderate-to-very strong positive relationship between TiO₂, Fe₂O₃, MgO, Na₂O, and P₂O₅, indicating that the destruction of clay, mica, amphibole, pyroxene, biotite, ilmenite, hematite, sphene, rutile, garnet, and apatite, along with calcium carbonate, manganese, and alteration minerals, contributed significantly to the composition of the river sand from this river catchment. The positive correlations between SiO₂, CaO, and K₂O indicated that they may have been derived from the same source. The elevated K₂O level may be related to the presence of secondary K-bearing minerals. The CaO content tended to increase downstream; however, the highest measured concentration in this river catchment was recorded at the sample site SS049. In the midstream regions, high contents of Al₂O₃, Na₂O, and P₂O₅ and the lowest concentrations of CaO and MnO were recorded. The reported distribution of the elemental concentrations near the downstream regions showed high measured values of TiO₂, Al₂O₃, Fe₂O₃, MgO, MnO, and P₂O₅. In contrast, elevated values of SiO₂, K₂O, and MnO were recorded at sample site SS049. The downstream regions also appeared to have high concentrations of SiO₂, Na₂O, and Al₂O₃ and low TiO₂ and CaO contents. These findings suggest that the midstream areas were largely influenced by quartz, clay, and mica contents as well as lithic fragments, which are associated with clastic sedimentary rocks. Near the downstream regions, clay, muscovite, quartz, plagioclase, chlorite, sphene, garnet and apatite minerals affiliated with clastic sedimentary rocks and their altered rocks owing to metamorphic processes made major contributions. However, sample location SS049 was characterized by notable inputs from quartz, muscovite, garnet, calcium carbonate, and manganese minerals, which were associated with clastic sedimentary interbedded with carbonate sedimentary rocks (such as micaceous shales and sandstones, marls and calcilutites) of the Wailuli Formation and their altered rocks due to metamorphic processes. In addition, there were major contributions from silicate and clay contents related to clastic sedimentary rocks in the downstream areas.

(10)

Sahe River catchment

The Sahe River catchment is covered by the Lolotoi Complex, Aitutu Formation, Wailuli Formation, Dartollu Limestone, Cablac Limestone, Viqueque Formation, Dilor Conglomerate, and Suai Formation (Figure 1C and Figure 3). The highest concentrations of CaO and K₂O, as well as the lowest values of Al₂O₃, SiO₂, MgO, Na₂O, and P₂O₅, were also registered in this river catchment (Table 1). CaO had a positive correlation with TiO₂ and MnO, and SiO₂ showed a very strong association with Al₂O₃, and they had a moderate-to-strong positive relationship with MgO, Na₂O, and K₂O (Table 2D). Positive associations were observed between TiO₂, Fe₂O₃, MnO, MgO, Na₂O, and P₂O₅. The presence of TiO₂ in carbonate sedimentary rocks associated with Mn minerals is not common. TiO₂ could be associated with Mn minerals in carbonate sedimentary rocks, suggesting the presence of secondary Ti-bearing minerals owing to certain alteration processes. In this river catchment, the highest concentrations of SiO₂ and K₂O appeared near the upstream areas, along with the lowest concentrations of TiO₂, Fe₂O₃, Na₂O, MnO, and CaO. Although high measured concentrations of SiO₂, K₂O, and MnO were reported in the midstream regions, sample location SS015 also appeared to have high measured contents of CaO and MnO and low concentrations of SiO₂, Al₂O₃, K₂O, and Na₂O. The downstream regions were also reported to have high SiO₂, Na₂O, K₂O, MgO, and MnO contents. This indicate that the composition of river sand sample near the upstream area was mostly controlled by the destruction of quartz, clay, and mica minerals, which were affiliated with clastic sedimentary rocks; however, silicate and accessory minerals (such as quartz, muscovite and garnet minerals), which are associated with their altered rocks due to metamorphic processes, contributed to the sample location SS013. Sample sites SS014 and SS015 had major contributions from calcium-carbonate minerals associated with carbonate sedimentary rocks of the Aitutu Formation and their altered rocks due to silicification or certain alteration processes [13,72,114]. There were notable inputs from quartz and secondary K-bearing minerals affiliated with altered carbonate sedimentary rocks intercalated with clastic sedimentary (e.g., shales) strata due to silicification processes in the sample location SS014, and considerable contributions to SS015 came from calcium carbonate, manganese, and Ti-bearing minerals, which were also associated with altered carbonate sedimentary rocks intercalated with clastic sedimentary (e.g., shales) strata due to certain alteration processes. The downstream regions were characterized by contributions from quartz, clay, carbonate, mica, amphibole, chlorite, ilmenite, garnet, and other minerals related to clastic sedimentary rocks.

5.3. Relationship between River Sand Geochemistry and Provenance Geology

The ratios of SiO₂/Al₂O₃ and K₂O/Na₂O, classification diagram of sediment using SiO₂/Al₂O₃ versus K₂O/Na₂O, and the geochemical index of ICV, are also frequently used to evaluate the abundance of quartz, clay, K-feldspar, plagioclase, and other less resistant minerals to identify provenance [50,52,90,92,94,115,116,117,118]. The SiO₂/Al₂O₃ ratio has different average values for determining source rock compositions and sediment maturities in clastic sediments; in basic igneous rocks, the ratio is approximately 3 and the ratio is approximately 5 in acidic igneous rocks. Hereafter, in clastic sediments, values >5 indicate compositionally mature sediments and values >10 indicate high maturity and potential recycling [53,92,94,117,119].

In the study area, the values of SiO₂/Al₂O₃ ratios ranged from 2.93 to 4.58, with an average of 3.59, slightly higher than PAAS but slightly lower than UCC (Table 1), suggesting that river sand compositions were not as silica and aluminum-rich as the average composition of typical crustal shale and granodiorite. The negative associations between the SiO₂/Al₂O₃ ratio and elements such as TiO₂, MgO, Fe₂O₃, Na₂O, and P₂O₅ (Table 2A–D) in most of the selected drainage basins, suggesting that these elements were not highly associated with silicate minerals but were incorporated into clay minerals. On the other hand, these elements showed a positive correlation with the SiO₂/Al₂O₃ ratio in the Sahe River catchment. This finding might also suggest that the geochemical composition of the river sand samples from this river catchment is significantly influenced by mineral contributions related to the presence of the Aitutu Formation’s clastic sedimentary rocks and their altered rocks as a result of silicification or other alteration processes.

The K₂O/Na₂O ratio also has variational values in defining the abundance of K-feldspar relative to plagioclase; with high values (>1) suggesting potential contributions from alkali feldspar or mica and/or possibly from secondary K-bearing minerals, whereas for the abundance of sodium-bearing minerals or plagioclase, the ratios were <1 [53,90,93,94]. The K₂O/Na₂O ratios in the study area ranged from 0.41 to 1.74, with an average of 0.73, which was much lower than those of UCC and PAAS (Table 1). Compared with the UCC, the K₂Oand Na₂O concentrations showed greater depletion, which could be related to the low contribution of feldspathic minerals [53,100,101]. These results indicated that the river sand content in the study area was also characterized by an abundance of aluminosilicate compared to feldspar. The highest values of the K₂O/Na₂O ratio (>1) were identified at several sampling points (Figure 6), which were mostly characterized by notable inputs from aluminosilicate and accessory minerals such as clays and muscovites. These minerals were mainly sourced from clastic sedimentary and metamorphic rocks rich in accessory minerals (e.g., muscovites), as well as shales, micaceous shales, micaceous sandstones, and their altered forms owing to metamorphic processes, which were affiliated with the Viqueque Formation, Dilor Conglomerate, and Wailuli Formation, respectively. However, sample locations SS014, and SS015 revealed features indicative of the presence of secondary K-bearing minerals and secondary Ti-bearing minerals associated with carbonate sedimentary intercalated with clastic sedimentary rocks that have undergone silicification and other alteration processes. These altered rocks are associated with the Aitutu Formations.

The geochemical classification binary diagram using SiO₂/Al₂O₃ against K₂O/Na₂O (Figure 7), proposed by Wimmenauer [118], showed that most of the river sand samples from the study area fall within the “pelitic greywacke” field, and only 4 samples stray into the “greywacke” field. This finding indicated that clastic sedimentary rocks (pelitic greywackes) also contributed significantly to the geochemical composition of most of the river sands in the study area.

Cox et al. [95] also determined ICV values greater than 1 for the sediments rich in non-clay minerals (chlorites, feldspars, amphiboles, and pyroxenes), whereas values less than 1 were found for sediments with significant concentrations of clay minerals (kaolinite, illite and montmorillonite) [50,53,90,92,94]. The ICV values in the study area ranged from 0.93 to 1.55, with an average of 1.26, which was much higher than those of PAAS and UCC (Table 1). The enrichments of TiO₂, Fe₂O₃, MnO, MgO, and P₂O₅ (Table 3 and Figure 5), as well as the positive association between these elements in most drainage basins (Table 2), corroborate the presence of mafic sources containing heavy and accessory minerals (such as amphibole, pyroxene, biotite, ilmenite, hematite, sphene, rutile, and garnet) [90,112]. These results revealed the abundance of chlorite minerals along with mafic, heavy, and accessory minerals in river sands from the study area. The occurrence of basic igneous and metamorphic rocks is mainly responsible for the contribution of these minerals to the research area. These rocks are affiliated with the Lolotoi Complex; however, they can be integrated into sedimentary rock fragments and matrices associated with the Aitutu, Wailuli, and Viqueque Formations and/or incorporated into mudstones and shales within the Bobonaro Complex as exotic blocks.

5.4. Principal Component Analysis

PCA was conducted on the major elemental compositions of stream sediments from the ten river catchments in the study area to determine their provenance. The first three principal components of the samples and variables with eigenvalues greater than or near 1.0 were processed for analysis and interpretation (Figure 8) [98,99]. The findings of the PCA were consistent with the results of the SiO₂/Al₂O₃ and K₂O/Na₂O ratios as well as those of the ICV.

The PCA results for the variables and samples are presented in

Table 4. Variable results on first three components of PCA. Variables selected are represented by loadings in bold and shaded cells.

	PC1	PC2	PC3
Eigenvalues	4.97	2.02	1.36
Explanation (%)	49.74	20.23	13.61
SiO2	0.2759	−0.4652	0.0452
TiO2	0.2586	0.4009	0.4187
Al2O3	0.4157	−0.1197	−0.2033
Fe2O3	0.3452	0.3725	0.1116
MnO	0.1122	−0.0577	0.7712
MgO	0.3553	0.2546	−0.3164
CaO	−0.4014	0.2846	0.0061
Na2O	0.3666	0.0892	−0.2309
K2O	0.1390	−0.5558	0.1306
P2O5	0.3336	0.0618	0.0602

and

Table 5. Sample results on first three components of principal compenent analysis (PCA). The samples selected are represented by loadings in bold and shaded cells.

	PC1	PC2	PC3		PC1	PC2	PC3
Eigenvalues	4.97	2.02	1.36	Eigenvalues	4.97	2.02	1.36
Explanation (%)	49.74	20.23	13.61	Explanation (%)	49.74	20.23	13.61
SS01	2.8094	−1.1265	0.3508	SS028	−1.0743	0.2423	−0.4641
SS02	0.9505	−1.3944	−0.3555	SS029	−6.2286	1.1078	−2.1250
SS03	−0.7047	0.9024	−0.5657	SS030	−2.8438	−0.1828	−1.0306
SS04	−4.2234	3.6410	−1.0284	SS031	−1.3621	−0.1580	−0.9280
SS05	−0.5243	0.3881	−0.0213	SS032	−0.8008	−1.1856	−0.7950
SS06	−4.0007	1.0310	−1.0535	SS033	−0.4160	−0.0219	0.4749
SS07	0.7688	0.1864	−0.3698	SS034	−0.2811	−0.8077	1.3272
SS08	0.2818	−0.1269	−0.4798	SS035	1.6275	−0.0210	0.6776
SS09	−1.1991	−1.9787	1.8580	SS036	−0.5419	0.0145	0.5499
SS010	0.2185	−0.3535	−1.6808	SS037	0.1410	0.5790	1.1977
SS011	−1.4795	1.3840	−0.6523	SS038	−0.6504	−0.8730	0.0325
SS012	−1.9347	−3.6500	−0.6833	SS039	−1.3181	−2.2499	−0.4070
SS013	−0.9795	−0.4875	2.2749	SS040	3.1957	−0.4899	−1.3336
SS014	−2.5533	−2.0583	−0.4066	SS041	3.1437	0.1735	−1.1314
SS015	−5.0541	2.0570	2.4259	SS042	3.1120	0.0048	−1.3984
SS016	−1.7343	0.1991	1.2251	SS043	0.6433	−2.2673	0.8850
SS017	0.2471	−1.2933	−0.5948	SS044	2.3801	0.5704	−1.1502
SS018	−0.0354	−1.2271	−0.3313	SS045	2.6404	2.3533	−0.4530
SS019	1.0377	1.6047	1.3011	SS046	2.2837	0.2010	−1.1381
SS020	1.8918	0.4021	1.0118	SS047	1.8602	0.2694	−1.5752
SS021	−0.2704	1.5562	1.8742	SS048	2.6183	0.4196	0.8197
SS022	2.5985	0.5487	−0.0845	SS049	−1.7195	−3.8376	2.6119
SS023	3.5647	1.1403	0.3147	SS050	3.2405	2.6371	2.5887
SS024	−2.1377	1.1255	−0.5264	SS051	2.1386	−0.1272	−0.6999
SS025	0.1876	1.5758	1.4588	SS052	2.3937	−0.3114	−0.7210
SS026	−1.7821	0.6782	−0.5172	SS053	0.6559	−1.1835	−0.5817
SS027	−0.7813	0.4200	0.0228

and in Figure 9 and Figure 10. The first, second, and third principal components accounted for approximately 49.74%, 20.23%, and 13.61% of the total explanations, respectively. The First Principal Component had a strong negative association with CaO (−0.40), especially for samples SS029 (−6.23), SS015 (−5.05), SS04 (−4.22), SS06 (−4.00), SS030 (−2.84), and SS014 (−2.55). Negative PC1 scores were attributed to the inputs from Ca-rich rocks. As the carbonate minerals were solely composed of CaO, it can be concluded that the carbonate components contributed more to the negative values of PC1. The abundance of carbonate components may be related to the presence of carbonate sedimentary (e.g., calcilutites, calcareous shales, and marls) and clastic sedimentary rocks rich in carbonate rock fragments in the Aitutu, Wailuli, Viqueque, and Ainaro Formations. PC1 had a strong positive correlation with Al₂O₃ (0.42), Na₂O (0.37), MgO (0.36), Fe₂O₃ (0.35), and P₂O₅ (0.33) for the samples SS023 (3.56), SS050 (3.24), SS040 (3.20), SS041 (3.14), SS042 (3.11), and SS01 (2.81). Ca-poor rocks were correlated with positive PC1 values. These samples were collected from clastic sedimentary rock-rich formations (e.g., shales, claystones, siltstones, sandstones, conglomerates, and mudstones), which are associated with the Wailuli, Viqueque, Suai, and Ainaro Formations and the Bobonaro Complex. Clay minerals rich in Al₂O₃, Na₂O, MgO, Fe₂O₃, and P₂O₅ in the clastic sedimentary rocks of these formations were highly positively correlated with PC1.

PC2 was strongly and positively associated with TiO₂ (0.40), Fe₂O₃ (0.37), CaO (0.28), and MgO (0.25), particularly in the following samples: SS04 (3.64), SS050 (2.64), SS045 (2.35), SS015 (2.06), SS019 (1.60), and SS025 (1.58). Input from SiO₂-poor rocks may explain the positive values of PC2. The elemental association of the positive values of PC2, possibly related to the contributions from mafic, heavy, and accessory mineral (such as amphiboles, pyroxenes, biotites, ilmenites, hematites, titanites, rutile, garnet, apatite, and others) inputs, is mainly attributed to the occurrence of igneous and metamorphic rocks in the study area. These rocks are associated with the Lolotoi Complex, but they may also be integrated into clastic sedimentary rock fragments and matrices associated with the Aitutu, Wailuli, Viqueque, Ainaro, and Suai Formations as well as the Dilor Conglomerate. These rocks may have also been incorporated into clastic sedimentary rocks (e.g., mudstones and shales) as exotic blocks within the Bobonaro Complex. Component 2 also had strong negative loadings for K₂O (−0.56) and SiO₂ (−0.47). Negative PC2 scores were observed for samples SS049 (−3.84), SS012 (−3.65), SS043 (−2.27), SS039 (−2.25), SS014 (−2.06), and SS09 (−1.98). SiO₂-rich rocks may have been responsible for the negative PC2 scores. The inputs of mica (muscovite) and quartz minerals may have contributed to the higher K₂O and SiO₂ concentrations, which consequently influenced the negative values of PC2. In the study area, these minerals are mostly ascribed to the existence of clastic sedimentary and metamorphic rocks (e.g., shales, micaceous shales and sandstones, conglomerates, sandstones, siltstones, claystones, mudstones, quartzites, and mica schists) of the Aitutu, Wailuli, Viqueque, and Ainaro Formations, Lolotoi Complex, and Dilor Conglomerate, as well as exotic blocks of these rocks from the Lolotoi Complex, Aitutu Formation, and Wailuli Formation within the Bobonaro Complex.

The third principal component had a strong positive loading for MnO (0.77), TiO₂ (0.42), K₂O (0.13), and Fe₂O₃ (0.11) and was strongly correlated with samples SS049 (2.61), SS050 (2.59), SS015 (2.43), SS013 (2.27), SS021 (1.87), and SS09 (1.86) (Table 4 and Table 5, Figure 10). The elemental association of positive PC3 scores may be associated with contributions from manganese, siderite, pyrite, secondary Ti-bearing minerals and K-bearing minerals. In the study area, these minerals were ascribed to the presence of exotic blocks of metamorphic rocks (e.g., garnet mica schists, mica schists, and quartzites) within the Bobonaro Complex; clastic sedimentary rocks (e.g., sandstones and conglomerates) rich in the Lolotoi Complex’s metamorphic rock fragments of the Dilor Conglomerate; and altered clastic sedimentary and carbonate sedimentary rocks intercalated with clastic sedimentary rocks (e.g., shales) due to metamorphic, silicification, and other alteration processes of the Wailuli and Aitutu Formations. Component 3 was also strongly associated in negative way with MgO (−0.32), Na₂O (−0.23), and Al₂O₃ (−0.20), and negative PC3 values were recorded for samples SS029 (−2.13), SS010 (−1.68), SS047 (−1.58), SS042 (−1.40), SS040 (−1.33), SS044 (−1.15), and SS046 (−1.14) (Table 4 and Table 5, Figure 10). The occurrence of secondary mineral assemblages in low-grade metamorphic conditions, such as chlorite, albite, and epidote, could influence the negative PC3 values by contributing greater amounts of MgO, Na₂O, and Al₂O₃. These river sand samples were collected from clastic sedimentary rock-rich formations (e.g., shales, sandstones, claystones, siltstones, conglomerates, and mudstones), which are affiliated with the Wailuli, Viqueque, Ainaro, and Suai Formations and the Bobonaro Complex.

6. Conclusions

This study showed the characteristics of the geochemical composition analysis and their relationship to the underlying lithology in the study area with limited geological information because of limited accessibility and dense vegetation coverage, as well as deformed, weathered, and erosion-covered materials. The areas covered by clastic sedimentary rocks are recognized higher concentrations of SiO₂, Al₂O₃, and K₂O. Meanwhile, the area covered by carbonate sedimentary rocks are detected by higher CaO and MnO. This study also contributed significantly to the discovery of altered clastic and carbonate sedimentary rocks within the Wailuli and Aitutu Formation in the midstream and near the downstream areas of the Clerec and Sahe drainage basins. These findings were identified by the increased contents and positive correlation between SiO₂, CaO, K₂O, and MnO, and CaO, TiO₂, and MnO in the areas. The contribution of quartz, accessory (e.g., muscovite and garnet), secondary K-bearing, and manganese minerals associated with clastic and carbonate sedimentary rocks, which may have undergone metamorphic and silicification processes, could account for the presence of SiO₂, CaO, K₂O, and MnO. The positive correlation observed between TiO₂, CaO and MnO may be ascribed to the presence of carbonate components associated with secondary Ti-bearing minerals, which are potentially formed through hydrothermal alteration processes. The occurrence of altered rocks and potential mineral resources associated with the Wailuli and Aitutu formations has never been reported or discovered in the surrounding areas of the Clerec and Sahe River catchments.

However, in another areas of Timor-Leste and the Indonesian west Timor region, Audley-Charles [13] and Barkham [114] have reported the existence of altered carbonate sedimentary rocks of the Aitutu Formation by silicification processes. Meanwhile, Vicente et al. [120] have presented the discovery of hydrothermal mineralization associated with Gondwana Megasequence in the Maquelab area (Oecusse - Timor-Leste). Further regional geochemical investigations in the study area are warranted, and the findings of this study could have implications for future lithological mapping research. Future geochemical mapping investigations are advised to focus on the Laclo do Sul, Clerec, and Sahe River catchments, which are covered by Wailuli and Aitutu Formations. In order to provide valuable information in mapping the distribution patterns of altered rocks and identifying potential mineral resources.