Orogenic and Post-Orogenic Gold Deposits: Spatiotemporal Distribution, Tectonic Controls, and Genetic Models

Abstract

Orogenic gold deposits represent the most important gold resource globally after Witwatersrand-style conglomerate-hosted gold systems and have remained a major focus of economic geological research and mineral exploration over the past few decades. This review systematically summarizes the spatiotemporal distribution, geological characteristics, tectonic controls, ore-forming material sources, and genetic models of orogenic gold deposits. Orogenic gold mineralization is closely genetically related to the assembly and evolution of global supercontinents, exhibiting three prominent episodic mineralization periods at 2.8–2.55 Ga, 2.1–1.8 Ga, and 600–50 Ma. These deposits are widely developed in Precambrian cratons and Phanerozoic orogenic belts and display strong diversity in host-rock lithologies, including greenstone belts, turbidite sequences, carbonate strata, and intermediate-felsic intrusions. Corresponding mineralization styles, wall-rock alteration assemblages, and trace element zoning vary systematically with formation depth, temperature, and pressure, forming a classic epizonal–mesozonal–hypozonal crustal-continuum metallogenic framework. Compressional settings dominate traditional orogenic mineralization, with ore formation controlled by ductile–brittle shear transition, crack–seal cycles, and fluid-stress coupling at different crustal levels. Increasing evidence suggests the gold deposits may also form in post-orogenic settings under extensional conditions, where tectonic activities can reactivate pre-existing orogenic structures and facilitate fluid migration and superimposed mineralization, although this category remains debated and represents an expanded interpretation of orogenic gold systems. In terms of ore genesis, three prevailing models, namely the crustal metamorphic devolatilization model, the basin-scale two-stage carbonaceous sediment-source model, and the deep-seated metamorphic metallogenic model, have been proposed. Meanwhile, increasing evidence also indicates that magmatic–hydrothermal fluids provide indispensable material and fluid contributions to some orogenic gold systems, although metamorphic fluids remain the widely invoked fluid source for most orogenic gold deposits. This contribution provides a comprehensive theoretical review for further genetic research of global orogenic gold deposits.

1. Introduction

Orogenic gold deposits, aside from the conglomerate-hosted gold deposits of the Witwatersrand Basin in South Africa, are the most important type of gold deposit in the world. They hold significant industrial value and have been one of the most critical targets for global mineral exploration over the past two decades. They also represent a major frontier research area in international economic geology over the last twenty years. The term “orogenic gold deposit” was first formally proposed by David Groves in 1998, encompassing deposit types previously described in the literature as greenstone belt-hosted gold deposits, turbidite-hosted gold deposits, ductile shear zone-hosted gold deposits, lode gold deposits, and metamorphic hydrothermal gold deposits [1]. The quartz-vein-type and altered-rock-type gold deposits, long widely used by academic and industrial communities, were also reclassified under the orogenic gold deposit category. The orogenic gold deposits are primarily distributed in Precambrian cratons and Phanerozoic orogenic belts. Typical examples of the former include the Superior Craton in North America, the Yilgarn Craton in Australia, São Francisco Craton in South America, and the West African Craton, while representative examples of the latter include the Central Asian Orogenic Belt, the North American Cordillera, the Lachlan Orogen in Australia, the Otago Orogen in New Zealand, and the West Qinling Orogen in China [2,3,4,5]. Some scholars also classify intrusion-related gold deposits within orogenic belts, those genetically associated with intrusions and temporally coincident with orogenesis, as orogenic gold deposits. Typical examples include intrusion-hosted gold deposits in the Alaska–Yukon region [2,4] and gold deposits associated with Late Devonian intrusions in the Stawell Mineral Field within the Lachlan Orogen, eastern Australia [6,7].

The researchers have conducted extensive studies on the orogenic gold deposits in the context of geological characteristics, geochronology, geochemistry, and metallogenesis. This paper provides a comprehensive review of the spatial and temporal distribution, mineralization styles, structural controls on mineralization, and genetic models of orogenic gold deposits [3,8,9,10,11,12,13,14,15]. This work synthesizes the supercontinent-controlled episodic peaks of orogenic and post-orogenic gold mineralization, contrasts compressional and extensional metallogenic regimes controlling gold mineralization, summarizes three dominant genetic models, and emphasizes the key role of magmatic–hydrothermal fluids in the formation of some orogenic gold deposits.

2. Definition of Orogenic Gold Deposits

Orogenic gold deposits refer to a class of gold deposits hosted in regional metamorphic terranes of various ages, formed during compressional to transpressional deformation processes at convergent plate margins, and genetically related to accretionary or collisional orogenesis (Figure 1; [1]). Accretionary orogens were formed during the subduction of oceanic crust beneath continental crust, whereas collision orogens generated by the amalgamation of continental blocks following the complete closure of intervening ocean basins. From an evolutionary perspective, both types of orogens mark the terminal stage of a crustal tectonic evolutionary cycle. Continental collision presupposes the closure of an ocean basin and represents the final stage in the evolution of accretionary orogens. It should be emphasized that orogenic gold deposits not only include those formed during orogenic processes, but also encompass those formed during terrane amalgamation processes in the Archean, at a time when modern plate tectonics had not yet been fully developed [13]. The term “orogenic gold deposit” unified various deposit types that had been confusingly used in earlier literature, including shear zone-hosted gold deposits, greenstone-hosted gold deposits, turbidite/slate-hosted gold deposits, and mesothermal lode gold deposits.

Figure 1. Tectonic setting of orogenic gold mineralization systems (modified from [16]).

3. Spatiotemporal Distribution of Orogenic Gold Deposits

Orogenic gold deposits exhibit significant temporal heterogeneity in their metallogenic epochs, characterized overall by episodic mineralization. Throughout Earth’s long geological history, orogenic gold deposits were concentrated in three key periods: 2.8–2.55 Ga, 2.1–1.8 Ga, and 600–50 Ma (Figure 2). These mineralization peaks coincide closely with episodes of rapid continental crust growth and are intimately related to the assembly and evolution of global supercontinents [2,17].

Figure 2. Temporal distribution of orogenic gold deposits in Earth’s history (after [5,18]). The colored shaded bands denote the periods of continental breakup events corresponding to the supercontinents including Ur, Kenorland, Columbia, Rodinia, and Gondwana/Pangea.

Currently, several orogenic gold deposits with formation ages older than 2.55 Ga (mainly 2.8 to 2.55 Ga) have been identified. They occur sporadically only in a few ancient geological units, such as the Barberton Greenstone Belt of the Kaapvaal Craton, the Ukrainian Shield, the São Francisco Craton [4,5], and the Pilbara Craton (Figure 3). Notably, the Barberton Greenstone Belt in South Africa hosts the oldest documented orogenic gold deposits (represented by the Fairview and New Consort deposits), which formed prior to ca. 3 Ga.

Orogenic gold deposits formed during the Paleoproterozoic (2.1–1.8 Ga) are linked to the assembly of the Columbia supercontinent. Orogenic gold deposits of this period occur both within cratonic greenstone belts and in metasedimentary sequences of craton-margin fold belts, including the Eburnean orogen of the West African Craton (Ashanti gold deposit) and the Trans-Hudson orogen of the North American Platform (Homestake gold deposit) (Figure 3).

During the prolonged period from the late Paleoproterozoic to the Neoproterozoic (1.8–0.6 Ga), spanning approximately 1.2 billion years, no economically significant orogenic gold deposits have been discovered globally, despite the occurrence of the Rodinia supercontinent assembly event. Only several orogenic gold deposits have been identified in the Jiangnan Orogen and Sunsás orogen during this period [19,20,21]. It remains challenging to interpret the scarcity of orogenic gold deposits during 1.7–0.75 Ga, which was termed as Earth’s middle age, using conventional accretionary-orogen uniformitarian models [2]. Well-established convergent boundaries along the margins of Laurentia and Baltica would have provided favorable, metal-enriched upper-mantle sources for forming these ore types. Long-term shifts in the occurrence of these deposits may stem from evolving lithospheric interactions linked to secular mantle cooling. Neoproterozoic and post-Neoproterozoic orogenic gold deposits formed via modern-type orogenic processes. By comparison, pre-1.7 Ga deposits originated in shallow-subduction settings; shear zones fragmented the mechanically weak lithosphere and served as principal conduits for gold-rich hydrothermal fluids [22].

Phanerozoic orogenic gold mineralization extended continuously from the late Neoproterozoic to the Eocene (600–50 Ma). In the early stage of Phanerozoic mineralization, orogenic gold deposits formed during collisional orogenesis along the active margins of Gondwana and Laurentia following the breakup of Rodinia. These deposits are mainly distributed in the Arabian–Nubian Shield [23], the Trans-Saharan Orogen of West Africa, the Brasília Fold Belt of the São Francisco Craton, the Siberian Platform, and the Paterson Orogen in Australia (e.g., the Telfer gold deposit) (Figure 3).

The episodic and heterogeneous distribution of orogenic gold deposits through geological time is primarily controlled by two key factors: crustal growth and evolution, and post-mineralization preservation conditions [17]. During the two major mineralization peaks at 2.8–2.55 Ga and 2.1–1.8 Ga, widespread mantle plume activity and mantle overturn events drove episodic rapid growth of Precambrian crust, providing the material and tectonic foundation for large-scale gold mineralization [2,3,8]. Moreover, the greenstone belts formed during these periods are mostly hosted within near-equidimensional, stable cratons, allowing them to be well preserved during subsequent long-term tectonic evolution without suffering intense erosion and destruction, thereby ensuring the preservation of the deposits.

Figure 3. Global distribution map of orogenic gold deposits with gold reserves exceeding 70 tonnes, modified after [24,25].

Figure 3. Global distribution map of orogenic gold deposits with gold reserves exceeding 70 tonnes, modified after [24,25].

4. Characteristics of Orogenic Gold Deposits

Systematic studies of global orogenic gold metallogenic belts/provinces have shown that orogenic gold deposits from different geological time periods and tectonic units exhibit strong similarities in terms of metallogenic tectonic setting, ore-forming geological conditions, ore mineral assemblages, alteration and mineralization characteristics, composition and properties of ore-forming fluids, and ore precipitation mechanisms [1,3,26,27]. However, many orogenic gold belts/provinces also display remarkable diversity in aspects such as host rock types and mineralization styles.

4.1. Crustal-Continuum Model

Based on long-term investigations of Archean gold mineralization in the Yilgarn Block, Western Australia, Groves [28] formally proposed the crustal-continuum model for orogenic gold systems. This empirical model was established on the widespread observation that orogenic gold deposits are not restricted to a single metamorphic environment but occur continuously across variable metamorphic grades, ranging from sub-greenschist facies to granulite facies. Accordingly, genetically linked orogenic gold deposits can form over a broad P–T range of 180–700 °C and 1–5 kbar, constituting a unified cogenetic metallogenic suite. Groves [28] summarized five key lines of evidence supporting the crustal-continuum model: (1) stable high-temperature and high-pressure metamorphic mineral assemblages; (2) zoned high-temperature minerals (e.g., diopside) in veins indicative of high-fluid-flux conditions; (3) complex morphological and textural variations of vein quartz and diopside; (4) consistent temporal relationships between host-rock metamorphism and gold mineralization in many districts; and (5) systematic vertical transitions in vein styles, wall-rock alteration, and mineral assemblages, reflecting continuous crustal metallogenic evolution. On the basis of formation depth and P–T conditions, orogenic gold deposits are further classified into three classical subtypes: epizonal deposits formed at depths <6 km and temperatures of 150–300 °C, mesozonal deposits at 6–12 km and 300–475 °C, and hypozonal deposits at depths >12 km and temperatures >475 °C.

Nevertheless, the crustal-continuum model has been questioned from a thermodynamic perspective. Phillips and Powell [9] argued that metamorphosed volcanic rocks may undergo partial melting at temperatures higher than 650 °C under hydrous conditions, whereas anhydrous metamorphic rocks are difficult to melt and cannot generate ore-forming fluids at high metamorphic grades. This mechanism challenges the feasibility of forming hypozonal orogenic gold deposits within granulite-facies terranes, implying that some high-grade metamorphic gold occurrences may represent overprinted rather than primary mineralization.

Despite its theoretical limitations in explaining ultrahigh-grade metamorphic mineralization, the crustal-continuum model remains the fundamental framework for understanding regional metallogenic zoning of orogenic gold deposits. From deep hypozonal to shallow epizonal levels, host-rock metamorphic grade, mineralization styles, wall-rock alteration, sulfide assemblages, and characteristic element associations exhibit continuous and regular transitions. This sequence corresponds to regional metamorphism within collisional orogens. With decreasing temperature and pressure, metamorphic facies shift from granulite and amphibolite facies through greenschist facies to prehnite–pumpellyite facies. Correspondingly, ore styles evolve from ductile-domain foliation-parallel deformed veins and coarse disseminated ores, through brittle–ductile crack–seal banded veins and en echelon vein arrays, to shallow brittle stockwork veins and hydrothermal breccia ores. Ore elemental associations also vary systematically from deep Au–As assemblages, through intermediate Au–As–Te–W associations, to shallow Au–Sb–Hg signatures, with Hg–Sb-dominated mineralization occurring at the shallowest crustal levels. The brittle–ductile transition at approximately 10 km depth represents the critical boundary corresponding to the greenschist–amphibolite facies transition. Importantly, this model describes regional-scale spatial metallogenic patterns rather than vertical zoning within individual ore districts, providing critical guidance for evaluating denudation degrees and regional exploration targeting [29].

4.2. Subtypes of Orogenic Gold Deposits Based on Host-Rock Type

Consistent with the crustal-continuum metallogenic framework, orogenic gold deposits develop in diverse lithological hosts, mainly including metamorphosed volcanic rocks, metasedimentary sequences, banded iron formations (BIFs) and granitic rocks [30]. Most gold mineralization is temporally and spatially coupled with greenschist-facies regional metamorphism, occurring synchronously with or shortly after peak metamorphism [10]. For example, the Mesozoic orogenic gold deposits in the Juneau gold belt (North America) are strictly hosted in greenschist-facies metamorphic belts, benefiting from the optimal matching between greenschist-facies P–T conditions and ore-fluid generation [31,32]. In contrast, individual deposits form in higher-grade metamorphic terranes, such as the Musselwhite amphibolite-facies-hosted gold deposit in the Abitibi Greenstone Belt. Additionally, carbonaceous and iron-rich strata act as effective chemical traps for hydrothermal metal precipitation, facilitating the formation of high-grade gold orebodies [10,30]. Based on previous classification criteria [33] and global comprehensive research, Wang [30] divided orogenic gold deposits into four lithology-based genetic types (Table 1), covering greenstone-hosted, turbidite-hosted, carbonate-hosted, and intrusion-hosted deposits, which fully reflect the lithological diversity of global orogenic gold systems.

Table 1. Characteristics of host-rock formation types for orogenic gold deposits (after [30]).

Deposit Type	Ore-Hosting Rocks	Represented Deposits	Mineralization and Alteration	Key Ore-Controlling Factors
Greenstone-Hosted type	Greenschist	Canada: Dome, Sigma, Lamaque, Porcupine; Australia: Golden Mile, Mt Charlotte; Suriname: Saramacca; India: Kolar	Orebodies occur as structural altered-rock types, quartz-vein types, stockwork and other types, and are mainly composed of various complex quartz–carbonate veins. Carbonate–sericite–pyrite alteration halos of variable widths are developed on both sides of orebodies. The assemblages and zonation of wall-rock alteration vary with host-rock types. The dominant sulfides in ores are pyrite ± arsenopyrite; pyrrhotite ± loellingite prevail under amphibolite-facies metamorphism. The Au/Ag ratios of ores are generally greater than 5, with enrichment of Ag-As ± W. Other commonly enriched elements include Hg, Sb, Bi, Mo, B and Te.	Deposits and ore fields are controlled by regional shear zones, and mostly occur in secondary shear zones adjacent to the main shear zones, especially where shear zones exhibit bends and intersections. Folds exert prominent ore-controlling effects, and orebodies can be localized in fold hinges, saddle zones, and fold limbs.
	Granite–gneiss	China: Jiaojia, Haiyu, Dahu, Wenyu, Paishanlou, Jiapigou and Hadamengou
	Banded Iron Formation	USA: Homestake; Tanzania: Geita; Mali: Gara; Canada: Lupin; China: Dongyaozhuang, Nanlongwangmiao.
	Others	Suriname: Rosebel; Mali: Sadiola Hill; Canada: Kerr Addison; China: Linglong, Shangong
Turbidite-hosted type	Sandstone–slate succession	Uzbekistan: Muruntau; Australia: Bendigo; Chinese: Sawayaerdun, Liba, Bagualiao, Jiagantan, Yangshan, and Woxi.	The alterations are mainly feldspathization, sericitization, carbonatization and biotitization. These deposits are characterized by Au enrichment with Au > As, and are associated with mineralization of As, W, Sb, Bi and Mo.	Similar to greenstone-hosted deposits, they exhibit more pronounced strata-bound features. Most shear zones occur along bedding or as low-angle interlayer shear zones, and some deposits are distinctly controlled by folds.
carbonate-hosted type	Carbonate–clastic rock succession	USA: Carlin; Canada: Tiger; China: Shuiyindong, Lannigou, Dongbeizhai, Jinlongshan and Manaoke.	Wall-rock alteration consists of medium–low-temperature assemblages including silicification, decarbonatization, argillization and dolomitization. Gold predominantly occurs as fine-grained invisible gold, with enrichment of As, Sb, Hg and Tl, and is accompanied by discrete Hg- and Tl-bearing mineralization.	Deposits are chiefly controlled by high-angle faults, anticlines and domes. Both strata-bound and fault-bound controls are important, and breccia pipes can be locally developed.
Shallow-intrusion-hosted type	Intermediate-felsic intrusions	USA: Fort Knox; Canada: Hollinger–McIntyre; Australia: Kanowna Bell; Guyana: Rory’s Knoll, Omai; China: Yu’erya, Niuxinshan, and Zaozigou.	Mineralization-related alteration is distinctly characterized by the development of K-feldspathization, albitization and silicification. The ore-forming element assemblages associated with mineralization are still dominated by As and Sb, together with W, Mo, Te, Bi, Pb and Ag.	The plutons are controlled by intersecting fracture structures, and mineralization is strictly confined within the extent of ore-forming plutons.

4.2.1. Greenstone-Hosted Gold Deposits

Greenstone-hosted gold deposits occur within Archean to Paleoproterozoic granite–greenstone metamorphic terranes and formed in the course of greenstone-belt development, evolution and subsequent tectonic reactivation. They can be further subdivided into three subtypes based on host rock association: (1) greenschist, (2) BIF, and (3) granite–gneiss. The greenschist subtype is dominated by mafic to ultramafic metamorphosed volcanic rocks. Prograde metamorphism from greenschist to amphibolite facies triggers large-scale devolatilization, releasing CO₂-rich fluids that mobilize gold from the strata. Typical examples include the Yilgarn Craton in Western Australia and the Abitibi Belt in Canada [34]. The BIF subtype exhibits strong stratigraphic control; iron oxides and sulfides in the BIF act as highly efficient geochemical barriers, capable of forming giant gold deposits such as Homestake and Geita. Orebodies are typically distributed along fold hinges and interlayer detachment zones [35]. The granite–gneiss subtype is hosted in TTG (Tonalite–Trondhjemite–Granodiorite) gneisses, amphibolites, and migmatites, with mineralization temperatures and pressures reaching 450–600 °C and 0.3–0.5 GPa. This type is developed in craton reactivation zones such as the Jiaodong and Xiaoqinling regions in China, where the time gap between regional metamorphism and gold mineralization can reach up to 2 billion years, and the ore-forming fluids contain contributions from mantle-derived components [36]. The contributions from mantle-derived components can also well explained their high formation temperature. Overall, greenstones exhibit significantly elevated background gold concentrations and constitute one of the most important primary gold source rock associations globally.

4.2.2. Turbidite-Hosted Gold Deposits

The host strata of turbidite-hosted gold deposits are dominated by Neoproterozoic–Paleozoic low-greenschist-facies carbonaceous slates, phyllites and meta-siltstones. Volcanic materials are extremely poorly developed. The organic-carbon contents of these strata generally range from 2% to 10%. Carbonaceous matter and syngenetic pyrite pre-concentrate gold during sedimentation and can serve as reducing agents for fluid-mediated gold precipitation during metamorphism. Orebodies mostly occur along bedding-parallel shear zones and fold detachment zones. The diagnostic element assemblage is Au-As-Sb-W. These deposits mostly occur within Phanerozoic collisional orogens. Their host rocks consist mainly of Neoproterozoic and Paleozoic shallow-marine turbidite successions. Compared with the host rocks of greenstone-belt gold deposits, they are characterized by scarce volcanic rocks and low metamorphic grades. Representative ore districts include Muruntau in Uzbekistan, Kumtor in Kyrgyzstan, the Sawayaerdun deposit in West Qinling and Southwest Tianshan of China, and Rodruin in Egypt [37,38,39]. Thick voluminous turbidite sequences constitute a material prerequisite for the formation of giant gold deposits. The total thickness of turbidites in the Muruntau ore district exceeds 4800 m, corresponding to gold resources of more than 6000 t [40].

4.2.3. Carbonate-Hosted Gold Deposits

Carbonate-hosted gold deposits are hosted in marine impure carbonate rocks intercalated with fine clastic strata. They experienced weak regional metamorphism and represent the shallow end-member (<6 km) of the crustal-continuum metallogenic model. Gold mainly occurs as fine-grained invisible gold within As-bearing pyrite, accompanied by the low-temperature element assemblage of As, Sb, Hg and Tl. Mineralization is jointly controlled by high-angle faults, anticline domes and breccia pipes. Ore-forming materials are all derived from the underlying Precambrian turbidite basement. Large-scale mineralization can hardly form without carbon-rich clastic source layers. Typical ore districts include the Carlin ore district in Nevada, USA, and the Youjiang Basin of the Yunnan–Guizhou–Guangxi region, China [41,42]. Such deposits commonly occur adjacent to turbidite-hosted gold deposits within the same orogenic belt and share identical metallogenic ages.

4.2.4. Intrusion-Hosted Gold Deposits

For intrusion-hosted gold deposits, ore-hosting media consist mostly of granite (porphyry), feldspar porphyry, feldspar–quartz porphyry, granodiorite (porphyry), diorite, diorite porphyry dikes, plutons or batholiths. Although these bodies do not belong to conventional strata, they are incorporated into the metallogenic spectrum as a special ore-hosting formation. K-feldspathization and albitization constitute diagnostic wall-rock alterations. Mixing between magmatic exsolved fluids and regional metamorphic fluids collectively drives mineralization. Orebodies are strictly confined within the plutons and their contact zones. These deposits frequently coexist with shear-zone-hosted vein-type gold deposits, and they serve as mutual exploration indicators. Typical examples are Omai and Aurora in Guyana, Yu’erya and Zaozigou in China, as well as Rodruin in Egypt. The “thermal-engine effect” induced by magmatic intrusion can enhance wall-rock permeability and promote gold remobilization from gold-source strata, acting as a critical overprinting condition for the generation of giant gold deposits [38,43].

4.3. Mineralization Styles

Orogenic gold deposits are mainly represented by quartz-vein and altered-rock types. Taking the Jiaodong gold province in China as an example, disseminated altered-rock-type deposits are predominantly distributed in northwestern Jiaodong. They are characterized by sericitization, silicification, sulfidation and K-feldspathization, with minor carbonate alteration, and are hosted within alteration zones along major regional faults. Gold-bearing quartz–sulfide vein-type deposits mostly occur in northeastern Jiaodong, hosted within distal NNE-NE-trending secondary faults parallel to the major regional faults [38,44,45,46,47,48,49].

In orogenic gold deposits, gold occurs dominantly as native gold, electrum, calaverite, and petzite, or as invisible gold in the form of solid-solution (Au⁺) or nanoscale native gold (Au⁰) hosted within pyrite [25,49,50,51,52]. Pyrite is the principal gold-bearing mineral, and gold is mostly concentrated in its microfractures [51,53,54,55]. Common ore minerals include pyrite, chalcopyrite, galena and sphalerite, which are closely associated with the main mineralization stage [40]. Gangue minerals mainly consist of quartz, carbonates, micas, albite, chlorite, pyrite, scheelite and tourmaline. The characteristic element assemblage is Au-Ag (As-Sb-Te-W-Mo), with generally low contents of Cu, Pb and Zn [10,25,56].

Apart from conventional vein-type and structural altered-rock-type gold deposits, other varieties may also develop, such as finely disseminated, breccia-type, carbonate-replacement-type, and intrusion-related gold deposits [3,57,58,59]. Such diversity of mineralization styles, especially the coexistence of multiple styles within a single district, has given rise to extensive controversies over the genesis of many orogenic gold deposits. A typical example is the Dashui gold deposit in the West Qinling orogenic belt. The alteration and mineralization features of the Dashui deposit differ markedly from most gold deposits in the West Qinling. For instance, its dominant ore mineral is hematite; ore grades are extremely high, with multiple high-grade ore intervals grading from hundreds up to several thousands of grams per tonne, and visible gold is abundant, whereas sulfides are extremely scarce. Alterations typical for orogenic gold deposits, such as clay alteration, K-feldspathization, sericitization, chloritization and iron carbonatization, are absent or poorly developed. Owing to these distinct mineralization features compared with classic orogenic gold deposits, substantial debate persists regarding its genetic type, ore-forming material sources and metallogenic epoch [60,61,62,63,64].

Variable mineralization styles of orogenic gold deposits within an orogen can reflect lithological differences in host rocks and local changes in metallogenic environments. They also constitute a direct manifestation of the diversity in ore-forming fluids and material sources for orogenic gold systems. In addition to widespread orogenic gold deposits, orogens host diverse types of metallic mineral deposits to varying degrees [65]. As exemplified by the West Qinling orogenic belt, besides gold deposits, it also contains Pb-Zn, Hg-Sb, Ba, U, Mo, W-Cu and other polymetallic mineral resources. Genetic types of these deposits cover orogenic, Carlin- and Carlin-like, porphyry, skarn, and SEDEX types [66,67,68]. Having undergone long-term accretionary orogenic evolution, the Central Asian Orogenic Belt hosts abundant orogenic, gold-rich porphyry, skarn, epithermal gold deposits and VMS-type gold-rich polymetallic deposits [69,70,71]. Unraveling the temporal–spatial relationships and potential genetic links between orogenic gold deposits and other gold deposit types represent an essential approach to constrain ore-forming material sources and metallogenic mechanisms, and to establish robust genetic models consistent with realistic geological constraints [65,72]. Nevertheless, research on this topic remains relatively limited and has not received sufficient attention.

The diversity of mineralization styles for orogenic gold deposits is closely linked to pronounced variations in metallogenic settings and physicochemical conditions. Based on metallogenic depth and P-T conditions, orogenic gold deposits can be further subdivided into three subtypes: epizonal (low-temperature, shallow), mesozonal (moderate-temperature, intermediate-depth), and hypozonal (high-temperature, deep). Their corresponding metallogenic depths are <6 km, 6–12 km and >12 km, with formation temperatures of 150–300 °C, 300–475 °C and >475 °C, respectively. Orogenic gold deposits formed under different depths and P-T conditions show systematic differences in alteration signatures, mineral assemblages, gold occurrence states, trace-element signatures of ores, and P-T constraints from fluid inclusions, and accordingly exhibit varied mineralization styles [1,3,28,65]. These diverse mineralization types can originate from a single regional metallogenic event at different crustal levels and be exhumed to a similar crustal level via post-mineralization differential crustal uplift; alternatively, they may result from superposition of multi-stage mineralization events. Accurately discriminating gold-deposit types with markedly different alteration–mineralization signatures is a critical unresolved issue for gold-deposit research in orogenic belts [19,62,73,74,75,76].

5. Tectonic Controls on Orogenic and Post-Orogenic Gold Deposits

5.1. Ore-Controlling Tectonic Regularities of Orogenic Gold Deposits Under Compressional Regimes

Groves [28] proposed the crustal-continuum metallogenic model, which argues that various metamorphic rocks ranging from sub-greenschist facies to granulite facies can generate cogenetic orogenic gold deposits. This model describes the overall regional-scale distribution of deposits rather than vertical mineralization zonation within a single ore district [29]. Based on this theoretical framework, orogenic gold deposits formed under compressional settings can be classified into deep-, intermediate- and shallow-level subtypes according to differences in tectonic deformation, P-T conditions, and fluid–rock coupling. Ore-controlling structures, alteration–mineralization features, and fluid evolution of deposits at different depths display a complete and continuously gradational sequence.

Hypozonal orogenic gold deposits (metallogenic depth > 12 km, temperature > 475 °C, ductile–brittle deformation): these deposits are hosted in amphibolite- to granulite-facies metamorphic rocks. Regional major thrust shear zones act as the primary ore-transmitting and ore-hosting structures. Orebodies are dominated by thick bedding-parallel lenses and large quartz veins. Wall-rock alteration is restricted to narrow zones, with an assemblage consisting of biotite, hornblende, plagioclase and quartz. Pyrrhotite, pyrite and chalcopyrite are diagnostic metallic minerals [77,78,79] (Figure 4).

Mineralization relies on the combined effect of super-lithostatic fluids with a high fluid factor (λ_v ≥ 1) and regional differential stress. K-feldspathization and silicification induce rock hardening, shift the rock failure envelope upward, and facilitate the generation of subhorizontal tensile fractures. Periodic hydraulic fracturing takes place via crack–seal cycles, and abrupt fluid-pressure drop triggers the synchronous precipitation of sulfides and quartz [80,81]. The Renco gold deposit in Zimbabwe is controlled by gently dipping, subhorizontal thrust shear zones [82], whereas the Hutti gold deposit in India preserves complete records of such crack–seal mineralization cycles [83,84,85]. Both are typical representatives of this deposit type.

Mesozonal orogenic gold deposits (metallogenic depth of 6–12 km, temperature of 300–475 °C, brittle–ductile transitional deformation): Orebodies are hosted in greenschist-facies strata at the critical brittle–ductile transition zone of the crust. After long-distance transport along deep major faults, fluids are emplaced in hinge voids of folds and R/R′/P Riedel-shear-derived fracture networks [86,87]. Orebodies are mostly saddle-shaped or pod-like, characterized by coexisting bedding-parallel veins and stockwork mineralization. Alteration zones show moderate widths, with a typical assemblage of chlorite–calcite–sericite–pyrite–pyrrhotite [88,89]. Sericitization softens wall rocks and reduces the rock failure threshold, thus shifting the rock failure envelope downward [80,81]. Fluid pressure drives the Mohr stress circle to shift leftward, and gold complexes decompose and precipitate within extensional-shear dilational spaces. The Betam gold deposit in Egypt is hosted in secondary shear fractures [88,90], whereas the Bendigo–Ballarat gold deposits in Australia formed within hinge voids of folds [87]. They serve as diagnostic examples of mesozonal deposits (Figure 4).

Figure 4. Tectonic ore-controlling styles of orogenic gold deposits under compressional regimes (after [85]).

Figure 4. Tectonic ore-controlling styles of orogenic gold deposits under compressional regimes (after [85]).

Epizonal orogenic gold deposits (metallogenic depth < 6 km, temperature of 150–300 °C, brittle deformation): These deposits are hosted in low-grade sub-greenschist-facies metamorphic rocks and are dominated by brittle fracture systems. Fold hinges, interlayer detachment zones and hydraulic breccia fracture zones constitute the main hosting spaces [86]. Orebodies occur as tabular and lenticular bodies, with breccia-type and disseminated mineralization as key features. Wall-rock alteration develops on a large scale, ranging from tens of meters up to one-thousand meters in width, typified by the sericite–carbonate–pyrite–arsenopyrite assemblage [29,79,91,92]. At shallow levels, fluids approach hydrostatic pressure with low migration rates, leading to sufficient water–rock interaction. Progressive sericitization weakens rock strength and shifts the failure envelope downward, triggering large-scale hydraulic fracturing and forming network-like and brecciated fluid-reservoir channels [80,81]. The Kharapeh gold deposit in Iran represents this deposit type [92] (Figure 4).

From deep to shallow metallogenic levels, orogenic gold deposits record a continuously transitional tectonic–mineralization–fluid sequence. Tectonic deformation evolves from deep ductile–brittle thrust–shear systems to shallow brittle-fracture and interlayer-detachment systems. Wall-rock alteration evolves from narrow high-temperature silicate alteration zones to broad low-temperature carbonate–sulfide alteration zones. Mineralization styles change sequentially from massive veins, through stockworks, to breccia-disseminated ores. Fluid processes transition from strong tectonic driving with weak water–rock reaction at depth toward weak tectonic constraint with intense water–rock interaction at shallow crustal levels. Three fluid-stress coupling mechanisms, namely crack–seal cycles, Riedel shearing and shallow-level hydraulic fracturing, control deposit emplacement at different crustal levels and collectively constitute the complete tectono-metallogenic system for orogenic gold deposits under compressional regimes [28,93].

5.2. Ore-Controlling Tectonic Regularities of Post-Orogenic Gold Deposits Under Extensional Regimes

The traditional view holds that orogenic gold deposits predominantly form under compressional and transpressional tectonic settings, and large-scale mineralization hardly occurs in purely extensional backgrounds [94]. Nevertheless, numerous case studies in recent years have demonstrated that fracture networks generated during the orogenic stage can be reworked and reactivated by later extensional tectonism, forming favorable sites for the migration and emplacement of ore-forming fluids [95,96]. According to rock-failure criteria, pre-existing fractures under extensional backgrounds follow two reactivation modes: preferentially oriented reactivation and differentially oriented hydraulic fracturing. Fluid pressure constitutes the key factor controlling fracture opening and fluid migration. On the basis of metallogenic depth, P-T conditions and deformation levels, orogenic gold deposits in extensional regimes can be divided into deep-, intermediate- and shallow-level subtypes. Typical examples include the Danba gold deposit along the western Yangtze margin, the Jiaodong ore district, Alaska-Juneau in Alaska, the Mingsai deposit in southern Tibet, and the Daqiao deposit in the West Qinling [55,88,97,98,99,100,101].

Hypozonal post-orogenic gold deposits (12–20 km, >475 °C, ductile–brittle deformation): Hypozonal gold deposits are hosted in amphibolite- and granulite-facies metamorphic rocks. Regional deep major faults serve as long-distance fluid migration channels, and secondary ductile–brittle shear zones govern orebody emplacement. Veins range from several meters to tens of meters in thickness and occur as stratiform-like and banded massive quartz veins. Wall-rock alteration is dominated by biotite, hornblende and plagioclase, with narrow alteration zones. Deep-seated fluids feature high pressure and rapid migration rates but weak water–rock interaction [77,79,97,98]. During the tectonic transition from compression to extension, the combined action of fluid pressure and differential stress shifts the Mohr-stress circle leftward, giving rise to preferentially oriented reactivation of pre-existing thrust faults [97]. Overpressured fluids migrate upward along lithosphere-scale faults via the crack-jump mechanism and precipitate ores within secondary fractures [95,102]. The Danba gold deposit on the western margin of the Yangtze Block represents a typical example of this subtype [97,98] (Figure 5).

Figure 5. Tectonic ore-controlling styles of post-orogenic gold deposits under extensional regimes (after [81]).

Mesozonal post-orogenic gold deposits (6–12 km, 300–475 °C, brittle–ductile deformation): Mesozonal gold deposits are hosted in greenschist-facies strata and controlled by reactivated normal faults, extensional tensile fractures and dilational jogs along fault bends. Veins are several meters to tens of meters wide, dominated by vein-type, fault-fill and stockwork orebodies, associated with moderately wide alteration zones comprising K-feldspar, sericite and pyrite [47,77,81,90,100,103]. In extensional settings, the maximum principal stress is nearly vertical (σ₁ = σ_v). Fluid pressure induces leftward shift of the Mohr-stress circle. When the Mohr circle becomes tangential to the failure envelope, two metallogenic paths are possible. First, pre-existing fractures undergo preferentially oriented reactivation; fluids trigger extensive alteration and precipitation at fault bends and discontinuities. The Xinli gold deposit in Jiaodong belongs to this category [47,103]. Second, elevated fluid pressure generates new vertical tensile-fracture networks, where fluids concentrate and form orebodies. The Alaska-Juneau gold deposit in Alaska serves as a representative case [85,100]. Sericitization reduces rock tensile strength and shifts the failure envelope downward, promoting fracture reactivation and fluid-driven mineralization [81,85] (Figure 5).

Epizonal post-orogenic gold deposits (2–6 km, 150–300 °C, brittle deformation): Epizonal gold deposits occur in sub-greenschist-facies or unmetamorphosed sedimentary rocks under dominantly brittle deformation. Fold hinges, interlayer detachments and hydraulic-breccia fracture zones constitute major ore-hosting structures. Orebodies are stratiform-like, tabular and lenticular, accompanied by broad-scale alteration assemblages of carbonate, muscovite and pyrite, characterized by breccia-type and disseminated mineralization [28,29,79,101,104,105,106]. Early silicified zones exhibit low permeability, leading to continuous fluid accumulation and pressure build-up. When fluid pressure exceeds the sum of the minimum principal stress σ₃ and rock tensile strength T, the Mohr circle shifts leftward and triggers hydraulic fracturing [98]. Fluids flow into breccia zones and rapidly decompress, resulting in gold unloading and precipitation. After fractures are cemented and sealed, fluids build pressure again. Repeated fracturing and superposition produce veinlet and breccia-style ores. The Daqiao deposit in the West Qinling and the Costerfield gold deposit are typical representatives [81,101,107,108] (Figure 5).

All gold deposits within extensional systems form by reactivation of pre-existing tectonic frameworks established during the compressional phase. Where the orientation of pre-existing fractures matches regional stress, reactivation and infill can take place under relatively low fluid pressure. Where orientations are mismatched, overpressured fluids are required to generate new fractures. With decreasing metallogenic burial depth, tectonic deformation transitions from brittle–ductile to brittle regimes, and mineralization styles evolve from thick massive quartz veins at depth, through stockworks at intermediate levels, to breccia-disseminated ores in shallow crust. Deep fluids are overpressured, strongly tectonically driven and marked by weak water–rock reaction, whereas shallow fluids approach hydrostatic pressure with markedly intensified metasomatic alteration.

6. Sources of Ore-Forming Materials and Genetic Models of Orogenic Gold Deposits

Numerous fluid-inclusion studies have demonstrated that ore-forming fluids of orogenic gold deposits are near-neutral, moderate-to-low-salinity C-H₂O fluids, generally with minor methane and nitrogen, and this property has reached a broad consensus [3,10,26,27,109]. Constraints on the origin of ore-forming fluids are mainly obtained by analyzing H-O-C isotopic compositions of hydrothermal gangue minerals equilibrated with ore-forming fluids. Bulk fluid-inclusion analyses (crushing or thermal decrepitation methods) yield a very wide range of hydrogen-isotope values of −179 to +7‰ [32]. However, these experimental techniques commonly extract fluid inclusions of multiple generations, and the obtained data represent mixed signals of multistage fluids, which cannot precisely characterize the hydrogen-isotope composition of primary fluids from the main mineralization stage [108]. Analyses of hydrogen isotopes from structural water in hydrous hydrothermal alteration minerals formed during ore deposition provide a more consistent range for ore-forming fluids: −80 to −20‰ [20,32]. In addition, some fluid-inclusion hydrogen-isotope values lower than −80‰ most likely reflect substantial enrichment of CH₄ in fluids [110,111,112,113,114].

Published isotopic statistics show that oxygen-isotope values of ore-forming fluids for Precambrian orogenic gold deposits cluster at 6‰–11‰ [26], whereas Phanerozoic deposits mostly yield δ¹⁸O values of 7‰–13‰ [32]. Such differences indicate distinctions in fluid source regions and rock geochemical properties of wall rocks traversed by migrating fluids. Carbon-isotope compositions of carbonate minerals and fluid inclusions from most orogenic gold deposits range from −11‰ to +2‰ [26]. Moreover, a considerable number of deposits show marked enrichment of ¹²C, which is widely interpreted as mixing with reduced organic carbon components [115,116].

Nitrogen isotopes constitute an effective tracer for constraining fluid sources. The most commonly analyzed minerals are muscovite, biotite and K-feldspar, in which nitrogen-bearing ammonium ions substitute for potassium within crystal lattices [3,10]. Available datasets yield nitrogen-isotope values of 10‰–24‰ for Neoarchean orogenic gold deposits [117,118], 6.5‰–12‰ for Paleoproterozoic gold deposits [119], and 1.5‰–5.5‰ for Phanerozoic orogenic gold deposits [120,121]. Radiogenic isotopes (Pb, Sr, Os), noble-gas isotopes and halogens have also been applied for fluid tracing, though far less widely than C-H-O stable isotopes. Furthermore, low abundances of these elements in ore-forming fluids leave their tracing reliability to be further validated and improved [10].

During mineralization of orogenic gold deposits, gold migrates dominantly as sulfur-bearing aqueous complexes [122,123]. Accordingly, Au and S are generally considered cogenetic. Gold has no stable isotopes, so sulfur isotopes are routinely used to constrain gold sources. Overall, orogenic gold deposits exhibit a wide scatter in sulfur-isotope values, yet the δ³⁴S values of most deposits cluster within 0‰–10‰ [3,10]. The sulfur-isotope evolutionary trend of Phanerozoic orogenic gold deposits correlates well with coeval seawater sulfate in host strata, implying that sulfur was derived from reduction of marine sulfate in sedimentary sequences and pyrite desulfurization during sedimentary diagenesis [31,124,125].

Three dominant genetic models have been proposed: crustal metamorphic devolatilization model [7], basin-scale two-stage mineralization model (carbonaceous sediment-source model; [126]), and deep-seated metamorphic metallogenic model [12]. Additionally, contributions of magmatic–hydrothermal fluids to orogenic gold mineralization have been increasingly reported in recent years [127,128,129] (Table 2).

Table 2. Diverse genetic models for orogenic gold deposits.

Genetic Model	Source of Fluid and Metal	Timing of Enrichment vs. Mineralization	Diagnostic Isotopic and Geochemical Evidence	Representative Deposits	Key Limitations
Crustal metamorphic devolatilization model	Fluids and metals derived from regional metamorphism of meta-volcanic and metasedimentary source rocks; no pre-mineralization metal enrichment in source sequences.	Ore formation occurs during prograde regional metamorphism (greenschist-facies P-T, brittle–ductile transition); metal mobilization and gold precipitation are nearly synchronous.	C-H-O isotopes consistent with metamorphic fluids; progressive depletion of Au-As-Sb-Hg in source rocks with rising metamorphic grade; sulfide breakdown releases trace metals.	Bendigo (Australia), Golden Mile (Kalgoorlie, Australia), deposits in Otago–Alpine belt (New Zealand), Superior metallogenic belt (Canada); Abu Gaharish (Egypt)	Struggles to explain deposits formed under amphibolite–granulite facies conditions; high-grade metamorphic overprint may erase original fluid/geochemical signals.
Basin-scale two-stage (carbonaceous sediment-source) model	Metals pre-concentrated in carbonaceous sedimentary sequences; sulfur from reduction of seawater sulfate. Fluids released during later metamorphism.	Stage 1 (sedimentary-early diagenesis): Au, As, Sb pre-enriched in arsenian pyrite within anoxic basins. Stage 2 (metamorphic remobilization): pyrite converts to pyrrhotite, releasing metals for ore formation.	In situ LA-ICP-MS pyrite trace elements; sulfur isotopes track seawater sulfate evolution; fluid inclusions contain CH4 and organic thermal-degradation products.	Sukhoi Log (Russia), Homestake (USA), Bodaybo (Russia), Carbon Leader (South Africa)	Mainly applicable to sediment-hosted orogenic gold; cannot readily account for greenstone-belt-hosted deposits. Some elements (Ni-Co-V-Cr) remain immobile during metamorphism and are not mobilized.
Deep-seated metamorphic metallogenic model	Ultimate fluid and metal sources: subducted oceanic crust, Au-rich pyritic sedimentary cover, metasomatized lithospheric mantle/mantle wedge.	Gold mineralization can take place under amphibolite- to granulite-facies high-T conditions; ore formation may postdate peak metamorphism of local wall rocks.	Isotopic data pointing to deep mantle-crust coupling; deposits preserve primary high-temperature mineralization signatures not derived from wall-rock devolatilization.	New Consort, Renco, Hutti, Navachab, Danba (western Yangtze margin), Beaver Dam (Canada), West Qinling and Huangjindong deposits (China)	The mantle-wedge and subducted crust metal flux is hard to quantitatively constrain; some geochemical signals may be overprinted by later metamorphism.
Magmatic–hydrothermal contributions (not an independent universal model)	Fluids and partial metals exsolved from middle-to-upper crustal magma chambers or deep magmatic sources; commonly mixed with metamorphic fluids.	Magmatic fluid input is synchronous with orogenic mineralization; may remobilize pre-existing gold or supply new metal components locally.	Os-He, noble gas, S isotopes showing mantle/magmatic mixing signals; fluid compositions with magmatic end-member fingerprints.	Muruntau (Central Asia), Loulo (West Africa), St Ives (Western Australia), Satinoco (Brazil), Hope Bay Madrid (Canada)	Magmatic fluids are not a global, universal fluid source; magmatic metal vs. remobilized gold is difficult to distinguish in many districts.

6.1. Crustal Metamorphic Devolatilization Model

With the continuous accumulation of global case studies, the crustal metamorphic devolatilization model (metamorphic devolatilization model; [7]) has gained increasing recognition. The core viewpoint of this model is that ore-forming fluids and metallogenic materials are derived from regional metamorphism of source rocks, which mostly refer to metamorphosed volcanic and sedimentary rocks without pre-enrichment signatures. During greenschist- to amphibolite-facies metamorphism, rocks release volatiles including H₂O, CO₂ and CH₄ as well as metallogenic elements such as Au and S to form metal-rich hydrothermal fluids. Gold precipitation and emplacement predominantly occur at greenschist-facies P-T conditions and at crustal depths corresponding to the brittle–ductile transition (Figure 6; [7,19,130,131,132]).

Figure 6. Crustal metamorphic devolatilization model (after [12]).

This model is consistent with field observations that many deposits are hosted in medium-to-high-grade metamorphic terranes. A typical example is the Bendigo gold deposit in the Victoria metallogenic province, Australia, which is hosted within greenschist-facies metamorphosed turbidites. Ore-forming materials and fluids originated from metamorphic devolatilization of a ca. 35 km thick meta-volcanic–sedimentary succession [133,134]. High-precision trace-element analyses of rocks with varying metamorphic grades from global metallogenic belts provide additional field geochemical evidence from the perspective of element mobility [135,136,137,138].

In the Otago–Alpine sedimentary–metamorphic belt of the South Island, New Zealand, the outer part consists of low-grade prehnite–laumontite-facies rocks, which grade inwards into pumpellyite–actinolite facies, lower greenschist facies, medium–high greenschist facies and lower amphibolite facies. Systematic analyses reveal that with increasing metamorphic grade from the periphery toward the core, rocks show progressive depletion in Au, Ag, As, Sb, Hg, Mo and W. The magnitude of depletion is tightly coupled with the breakdown of pyrite, sphalerite, galena and cobaltite. This indicates that metamorphic heating drives phase transformation and decomposition of sulfides, leading to trace-element remobilization. Regional gold deposits are concentrated within schist belts, and the trace-element assemblages of ores match well with components leached from wall rocks, demonstrating that metamorphically remobilized metals migrated along faults to form deposits. Metasedimentary rocks in the Superior metallogenic belt of the Canadian Shield also display decreasing whole-rock gold contents at higher metamorphic grades, supporting gold remobilization during prograde metamorphism [128].

Analyses of basaltic rocks from the Otago–Alpine belt show that meta-basites have comparable gold-release capacities relative to metasedimentary rocks, but cannot supply arsenic. Studies on volcanic rocks from the La Grande metallogenic province in Canada and the Central Lapland greenstone belt in Finland demonstrate that 77% and 59% of primary gold was released respectively during amphibolite-facies metamorphism, confirming metamorphosed volcanic rocks as high-quality source rocks [138]. Petrological experimental data provide further support: simulations by Phillips [139] indicated that devolatilization of greenstone-belt meta-basites at amphibolite facies could supply CO₂, K, S, H₂O and Au required by the Golden Mile deposit in the Kalgoorlie goldfield. Using the CaO-MgO-FeO-Al₂O₃-SiO₂-H₂O-CO₂ system, Powell [140] modeled meta-basic and meta-ultrabasic rocks and found that high-greenschist- to low-amphibolite-facies metamorphism can generate low-salinity CO₂-rich fluids, which perfectly match fluid signatures of greenstone-belt gold deposits. The Archean crust was characterized by relatively small thickness, high heat flow and widespread volcanic rocks, which provided favorable prerequisites for mineralization from metamorphosed volcanic rocks. Meanwhile, the Archean atmosphere was anoxic with weak continental weathering, so clastic sedimentation was far less extensive than in the Phanerozoic [141,142,143].

Several deposits hosted within high-grade metamorphic terranes, including Big Bell and Griffin’s Find in Western Australia, Renco in Zimbabwe, Challenger in South Australia and Hemlo in Canada, cannot be explained by the crustal-continuum metallogenic model. According to the metamorphic devolatilization model, these deposits initially formed under greenschist-facies conditions and both orebodies and wall rocks were subsequently overprinted by granulite-facies metamorphism. Thermodynamic modeling by Tomkins [143] illustrated gold mobility within Fe-bearing sulfides during prograde and retrograde metamorphism. The results verify that gold deposits within high-amphibolite- to granulite-facies rocks of the Gawler Craton represent products of early-stage mineralization overprinted by later high-grade metamorphism.

6.2. Basin-Scale Two-Stage Mineralization Model (Carbonaceous Sediment-Source Model)

Large [144] performed LA-ICP-MS in situ analyses on pyrite of diverse genetic origins from the Sukhoi Log gold deposit in the Russian Far East. Sediment-derived pyrite is markedly enriched in Au, Mo, Sb, Ni, Co, Se, Te, Ag, Cu, Pb and Zn. Trace-element contents decrease progressively in diagenetic, metamorphic and hydrothermal pyrite generations, which commonly contain inclusions of native gold and sulfide minerals. Subsequent studies refined the two-stage metallogenic theory: pyrite pre-concentrates metals during sedimentary–early diagenetic stages, and regional deformation and metamorphism trigger desulfurization of pyrite to form pyrrhotite, releasing metallogenic materials for ore emplacement [145,146].

This model involves two evolutionary steps: (1) Sedimentary–diagenetic stage: Within reduced, anoxic epicontinental basins, organic matter adsorbs Au, As, V, Ni, Se, Ag, Zn, Mo, Cu and U from water columns. These elements are concentrated in fine-grained black mudstone and siltstone of slope and basinal facies. During early diagenesis, Au, Ni, Se, Te, Ag, Mo, and Cu (accompanied by PGEs) are incorporated into arsenian pyrite, forming extensive Au-As-rich source beds. Rock Au concentrations generally range from 5 to 100 ppb, and As from 10 to 200 ppm. Local arsenian pyrite can contain up to 1–2 ppm Au and 1000 ppm As, and may host nanoscale native gold. During late diagenesis to early metamorphism, fine-grained arsenian pyrite recrystallizes, and organic matter transforms into bitumen. (2) Metamorphic remobilization stage: Under P-T conditions of lower greenschist facies and above, arsenian pyrite converts to pyrrhotite and releases Au, As, Sb, Te, Cu, Zn, Mo, Bi, Tl and Pb. Hydrothermal fluids transport these components and concentrate them along favorable structures to form economic orebodies.

Strong depletion of Au and As in deep-seated pyrrhotite from the Bendigo mining district, Victoria, is consistent with predictions of this model [147]. With the widespread application of in situ microanalytical techniques, pre-enrichment of ore-forming elements in pyrite from carbonaceous clastic rocks has been documented in many typical global mining districts: Bodaybo in Russia [148], Homestake in USA [149], Yukon in Canada [150], Golden Mile in Australia [151], Otago in New Zealand [152], and Carbon Leader in South Africa [153].

In situ S- and Pb-isotope measurements and quantitative fluid-inclusion analyses continuously support this model. Chang [125] analyzed sulfur isotopes of multistage pyrite from the Sukhoi Log gold deposit. Early-stage values show scattered distributions, whereas late-stage data converge toward a stable mean, indicating sulfur derived from seawater sulfate reduction and isotopic homogenization driven by metamorphism. Sulfur-isotope signatures of global sediment-hosted gold deposits correlate well with coeval seawater sulfur evolution, corroborating that sulfur (gold migrates as bisulfide complexes) originates from sedimentary–diagenetic pyrite. In situ Pb-isotope data from Meffre [154] also support the two-stage evolutionary model. Gaboury [155,156] compiled fluid compositions of typical global deposits, where CH₄, C₂H₆, CO₂, SO₂ and H₂S are widely detected. These species correspond to thermal degradation, hydrolysis and oxidation of organic matter, confirming the suitability of organic-rich sedimentary rocks as source rocks.

Limitations in applicability: This model targets sediment-hosted gold deposits and does not cover greenstone-belt-type deposits [145]. The Second Great Oxidation Event (635–510 Ma) increased the solubility of deep-ocean sulfate and gold. Bacterial sulfate reduction generated Au-rich pyrite and formed large-scale Phanerozoic source beds [9]. Studies of the Ballachulish metamorphic aureole in Scotland demonstrate that metamorphism from greenschist to amphibolite facies remobilizes Au-As-Bi-Sb-Mn-W, while Ni-Co-Mo-V-Cr-Cu-Pb-Zn remain retained within neoformed minerals. Sulfur released during pyrite-to-pyrrhotite conversion preferentially combines with Fe in silicates, and meta-basic–ultrabasic rocks yield limited sulfur [157]. Thermodynamic simulations supplement mechanistic understanding: chlorite decomposition produces water and increases fluid demand, facilitating pyrite phase transformation and sulfur release. Mudrocks preferentially release Au and minor base metals during metamorphism, which accounts for the general low base-metal signatures of orogenic gold deposits [84,94].

The key differences between the two dominant models are as follows [146]: (1) Material source: The two-stage model advocates primary gold enrichment within sedimentary basins; the metamorphic devolatilization model argues that source rocks lack pre-enrichment and metals are remobilized integrally during metamorphism. (2) Role of carbonaceous rocks: The former considers organic-rich sedimentary rocks as the material source; the latter treats them as carriers for metal precipitation. (3) Metallogenic timing: The former involves early sedimentary pre-enrichment followed by remobilization and ore emplacement during metamorphism; the latter features one-shot ore formation during late orogenic metamorphism.

6.3. Deep-Seated Metamorphic Metallogenic Model

The metamorphic devolatilization model assumes that gold deposits within high-grade metamorphic facies initially formed under greenschist-facies conditions and were subsequently overprinted. However, several deposits including New Consort, Renco, Hutti and Navachab demonstrably formed under amphibolite- to granulite-facies conditions [158,159]. Phanerozoic deep-seated gold deposits such as Danba along the western Yangtze margin, Beaver Dam in Canada’s Meguma Belt, and deposits in the French Massif Central exhibit primary high-temperature signatures and are not products of prograde metamorphic devolatilization of wall rocks. Some deposits formed after high-grade metamorphism of their host rocks; the wall rocks had already completed devolatilization and could no longer supply ore-forming materials (e.g., Cenozoic gold deposits in the Mexican Megashear Belt). Certain deposits in West Qinling, the Huangjindong deposit in the Jiangnan Orogen, and parts of the Ailaoshan metallogenic belt also cannot be interpreted by the former two models. Building on research results from the Jiaodong gold province [36], Groves [12] proposed the deep-seated metamorphic metallogenic model. In this model, subducted oceanic crust, overlying Au-rich pyritic sedimentary sequences, and metasomatized lithospheric mantle/mantle wedge represent the ultimate sources of ore-forming fluids and metals. This model can theoretically account for the genesis of orogenic gold deposits worldwide (Figure 7; [96]).

Figure 7. Deep-seated metamorphic metallogenic model (after [14]). The diagram showing the major host-rock types of orogenic gold deposits (modified from [30]).

6.4. Contribution of Magmatic–Hydrothermal Fluids into the Orogenic Gold Mineralization

Magmatic–hydrothermal fluids cannot act as a universal ore-fluid source on a global scale; nevertheless, numerous case studies confirm the involvement of magmatic components in mineralization within individual mining districts [16]. Os-He isotopes of arsenopyrite from the Muruntau gold deposit in Central Asia (with reserves exceeding 6000 t) indicate mixing of mantle-derived magmatic fluids [126,127,128]. Ore-forming fluids in the Loulo goldfield of West Africa show mixed signatures of metamorphic and magmatic end-members [116,156]. Mass-independent fractionation signatures in pyrite from Archean mining districts imply that sulfur and gold were sourced from deep magmatic chambers or the mantle [159,160,161]. Noble-gas isotopes from the St Ives gold deposit in Western Australia demonstrate fluid links with crust-derived magmas [162]. Mineralization temperatures at the Satinoco gold deposit in Brazil were controlled by granitic magma emplacement, with direct participation of magmatic–hydrothermal fluids in ore formation [162]. Pre-existing mineralization at the Hope Bay Madrid gold deposit in Canada was overprinted by magmatic fluids to form high-grade orebodies, though it remains unclear whether metals were remobilized in situ or supplied by magmatic transport [163]. Goldfarb and Groves [10] concluded that magmatic–hydrothermal involvement in mineralization is real under specific tectonic settings, and fluids exsolved from upper-to-middle crustal magma chambers as well as deep-seated fluids can provide metallogenic materials [5,40,163,164,165,166,167,168].

A commonly confused deposit type also occurs within accretionary orogens: intrusion-related gold deposits. Representative examples include Cretaceous deposits such as Fort Knox and Donlin Creek along the Tintina fault zone of the Cordilleran orogen, and Late Devonian intrusion-associated gold deposits in the Stawell goldfield of the Lachlan Orogen, Australia [56,57,165]. Their key diagnostic features are summarized below: (1) Tectonic setting: Accreted terranes at convergent continental margins, located toward the intracontinental side rather than in island-arc belts. (2) Associated mineralization: Frequently co-occur with W-Sn mineralization within the same igneous province. (3) Intrusion characteristics: Granodioritic-to-granitic subalkaline rocks ranging from metaluminous to weakly peraluminous. Crustal components increase magma reducibility and favor gold enrichment. (4) Zonation pattern: A complete elemental zonation from high-temperature magmatic to low-temperature hydrothermal conditions centered on the intrusive body. (5) Ore styles: Greisen-type, disseminated, sheeted-vein, stockwork and breccia-hosted mineralization developed inside plutons; vein-type, disseminated and replacement orebodies formed in wall rocks. (6) Alteration assemblages: Quartz, K-feldspar, albite, sericite and carbonatization. (7) Sulfide characteristics: Low total sulfide contents with depleted base metals; mineral assemblages dominated by pyrrhotite, pyrite, loellingite and arsenopyrite. (8) Characteristic elements: Enrichment in Bi, W, As, Sn, Mo, Te and Sb; gold is commonly associated with Bi-tellurides, accompanied by molybdenite and scheelite. (9) Fluid properties: Wide salinity range and overall CO₂-rich signatures.

7. Conclusions

Orogenic gold deposits are universally formed during accretionary and collisional orogenic processes and constitute a continuous crustal-scale metallogenic system spanning sub-greenschist to granulite metamorphic facies. Their global spatiotemporal distribution is episodic and controlled jointly by crustal growth events, supercontinent assembly, and post-mineralization preservation conditions. Significant metallogenic diversity is manifested by variable host rock associations, mineralization styles, alteration sequences, and element geochemical signatures, which correspond to distinct physicochemical conditions at shallow, intermediate, and deep crustal levels. Tectonic deformation and fluid–rock coupling are the core controls on gold precipitation. In compressional orogenic environments, systematic transitions from deep ductile–brittle shear mineralization to shallow brittle fracture and breccia-hosted mineralization form a complete vertical metallogenic zoning sequence. In extensional tectonic settings, reactivation of inherited orogenic structures and fluid overpressure-driven fracturing trigger superimposed gold mineralization, greatly expanding the metallogenic potential of traditional orogenic belts. Currently, three mainstream genetic models have been proposed. The metamorphic devolatilization model emphasizes in situ fluid and metal release from regional metamorphism; the two-stage sedimentary source model highlights early diagenetic metal pre-enrichment in carbonaceous basins followed by metamorphic remobilization; and the recently proposed deep-seated metamorphic model integrates subducted oceanic crust, sedimentary sequences, and metasomatized mantle wedge materials to explain high-grade metamorphic and supergene orogenic gold mineralization. In addition, magmatic–hydrothermal fluids are increasingly recognized as important auxiliary metallogenic components in specific accretionary orogens. Future research should focus on finely characterizing the coupling mechanisms between multistage tectonic transitions and fluid evolution, identifying the key controlling factors of mineralization style diversity, clarifying the material contributions of deep mantle sources and magmatic overprinting, and establishing unified genetic criteria to distinguish diverse orogenic gold subtypes. The integrated application of petrology, geochemistry, and in situ isotopic constraints will further refine the metallogenic theory of orogenic gold systems and provide guidance for future regional gold exploration. This study systematically summarizes the metamorphic facies, vein styles and elemental signatures of different orogenic gold deposit types formed at varying crustal levels. These discriminative criteria enable precise discrimination of deposit genetic type and mineralization crustal level. Together with regional geological constraints for targeting favorable ore-forming sites and denudation assessment to evaluate ore preservation, they offer clear theoretical guidance for delineating regional exploration targets and vectoring toward high-grade mineralized zones.