The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle
Abstract
:1. Introduction
2. Geological Background and Description of the Investigated Chromitite
3. Analytical Techniques
4. Mineral Descriptions and Compositions
4.1. Chromitite and Chromite
4.2. Rutile
4.3. Zircon
4.4. PGM, Au and Ag Phases
4.5. Other Accessory Minerals
5. Discussion
5.1. Origin of the Cedrolina Chromitite
- The Cedrolina chromitite is podiform, and therefore associated with a Precambrian ophiolite. In this case, it would imply that either the parental magma of the chromitite (rich in Ti) was chemically different from all other magmas associated with ophiolitic complexes known to date (low Ti) or that titanium was added by external sources/fluids and the internal polygonal texture of nodules is solely due to metamorphic recrystallization.
- The Cedrolina chromitite is stratiform, hence associated with mafic–ultramafic (high Ti) intrusions. If this alternative is valid, the structure observed in chromite could be understood as a new type of metamorphic orbicular structure that has not been described in the literature. The chromite nodules may have been formed by aggregates of fine euhedral chromite crystals resembling a cumulus texture as shown in Figure 4B–D. The straight contacts, as well as the triple junctions as shown in Figure 4D, may represent an original cumulus texture which was not completely obliterated by recrystallization. This observation could constitute another argument in favour of a cumulitic-stratiform origin.
5.2. The Accessory Minerals in the Cedrolina Chromitite and Their Petrogenetic Significance
6. Conclusions
- The Cedrolina chromitite exemplifies a completely metamorphosed chromitite.
- The main regional metamorphic peak reached the low amphibolite facies, with temperatures of 550–600 °C at an estimated pressure range of 0.4–0.6 GPa. This event was responsible for the complete obliteration of chromite magmatic composition.
- Among the studied accessory minerals, only irarsite and laurite could be relicts of the primary igneous assemblage, whereas Au–Pd and Au–Cu–Ni compounds are likely products of low-temperature remobilization and recrystallization of the igneous phase, arguably under weathering/supergene conditions.
- The precipitation of exotic accessory minerals found in the Cedrolina chromitite is probably related with metasomatism promoted by hydrothermal fluids derived from a granitic intrusion that occurs in the same area. Although not confirmed, this theory is supported by accessory zircon (found in the chromitite) trace element composition, which suggests a granitoid source.
- Rutile likely formed due to Ti remobilization from Cr-spinel after/synchronously to chromite deformation/fracturing during the main metamorphic and deformational event (Dn). Geothermometric calculations resulted in a crystallization temperature range of 510–670 °C (averaging 550–600 °C at an estimated pressure range of 0.4–0.6 GPa) concordant with an upper greenschist to low amphibolite facies metamorphic grade. Thus, it suggests that the magmatic composition of chromite could have been originally higher in Ti, indicating a stratiform origin. Alternatively, the Ti-enrichment could have been caused by external metasomatic infiltrating fluids leading to the formation of rutile. If this was the case, the Cedrolina chromitites could be classified as podiform, possibly representing a sliver of tectonically dismembered Paleoproterozoic upper mantle.
- The nodular structure observed in the Cedrolina chromitite resembles those described in ophiolitic chromitites. However, it could also be interpreted as a new type of metamorphic structure which was not previously described in literature. The orbs feasibly formed by post-magmatic and partial recrystallization processes, however, it is still unclear to what extent metamorphism controlled recrystallization due to the poly-metamorphic history of the area.
- The Cedrolina chromite composition in terms of Cr# and Mg# plots outside the fields of both podiform and stratiform chromitites, being characterized by high values of Cr# and low Mg#. They display a very restricted and highly refractory composition of Cr-spinel (high Cr#). Therefore, it differs from the Neoproterozoic ophiolitic chromitite of the Eastern Desert of Egypt and Saudi Arabia [35,36,37,38] that can be classified as Cr- and Al-rich. Regarding their TiO2 content, few analyses of the Cedrolina chromitite plot in the field of stratiform chromitite (occurring in layered complexes).
- The strong metamorphic overprint that affected the studied chromitites has made it dubious to define their original geodynamic setting and to properly classify them as podiform or stratiform.
Acknowledgments
Author Contributions
Conflicts of Interest
References
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Sample CED | SiO2 | Al2O3 | MgO | FeO | Cr2O3 | Total |
---|---|---|---|---|---|---|
47A | 32.92 | 14.18 | 32.36 | 1.89 | 3.78 | 85.13 |
47A | 33.34 | 13.76 | 33.02 | 2.23 | 4.20 | 86.55 |
47A | 31.57 | 16.03 | 31.88 | 2.41 | 4.25 | 86.14 |
47A | 33.09 | 13.71 | 33.03 | 2.01 | 3.93 | 85.78 |
47A | 32.77 | 13.91 | 32.90 | 1.80 | 3.99 | 85.36 |
47A | 30.93 | 16.53 | 31.21 | 2.31 | 3.85 | 84.83 |
47A | 32.92 | 14.57 | 32.47 | 1.99 | 4.03 | 85.97 |
47A | 29.92 | 17.66 | 30.85 | 2.24 | 4.17 | 84.84 |
105C | 29.52 | 17.06 | 31.21 | 2.26 | 3.30 | 83.35 |
105C | 28.62 | 18.87 | 30.22 | 2.30 | 3.40 | 83.41 |
105C | 29.25 | 18.03 | 29.40 | 2.54 | 3.96 | 83.18 |
105C | 30.02 | 15.98 | 30.90 | 2.17 | 3.95 | 83.02 |
105C | 30.26 | 16.29 | 31.87 | 2.11 | 3.62 | 84.14 |
106D | 31.70 | 17.60 | 27.99 | 4.10 | 2.13 | 83.52 |
106D | 32.10 | 17.92 | 29.25 | 3.94 | 1.99 | 85.21 |
106D | 32.06 | 19.22 | 28.19 | 3.51 | 2.19 | 85.17 |
106D | 29.86 | 20.30 | 27.43 | 4.02 | 2.47 | 84.09 |
106D | 31.15 | 17.35 | 29.79 | 3.78 | 2.10 | 84.17 |
Sample CED | Al2O3 | Fe2O3 | Cr2O3 | FeO | MgO | MnO | TiO2 | V2O3 | Total |
---|---|---|---|---|---|---|---|---|---|
100 | 8.1 | 9.7 | 49.51 | 29.83 | 1.89 | 0.78 | 0.25 | 0.16 | 100.22 |
100 | 6.66 | 11.03 | 49.89 | 30.47 | 1.58 | 0.76 | 0.41 | 0.17 | 100.97 |
100 | 5.78 | 12.45 | 50.2 | 30.17 | 1.48 | 0.92 | 0.15 | 0.16 | 101.31 |
100 | 7.79 | 10.83 | 49.15 | 30.28 | 1.75 | 0.77 | 0.3 | 0.12 | 101 |
105A | 5.48 | 3.25 | 59.16 | 27.22 | 3.2 | 0.66 | 0.06 | 0.16 | 99.18 |
105A | 10.05 | 3.24 | 55.15 | 27.43 | 3.89 | 0.56 | 0.1 | 0.19 | 100.6 |
105A | 5.82 | 3.04 | 60.1 | 27.42 | 3.37 | 0.64 | 0.05 | 0.18 | 100.6 |
105A | 6.56 | 3.75 | 58.24 | 27.03 | 3.64 | 0.62 | 0.02 | 0.11 | 99.97 |
105A | 10.16 | 0.68 | 55.56 | 28.29 | 3.95 | 0.52 | 1.1 | 0.23 | 100.48 |
105B | 8.66 | 5.57 | 54 | 25.64 | 4.55 | 0.67 | 0.12 | 0.19 | 99.39 |
105B | 7.57 | 4.85 | 55.58 | 26.61 | 4.37 | 0.62 | 0.65 | 0.17 | 100.43 |
105B | 4.44 | 4.38 | 60.81 | 26.79 | 3.64 | 0.67 | 0.02 | 0.19 | 100.93 |
105B | 5.53 | 4.62 | 59.67 | 25.96 | 4.28 | 0.63 | bd | 0.12 | 100.82 |
105C | 5.81 | 2.5 | 60.75 | 25.12 | 4.74 | 0.67 | 0.03 | 0.11 | 99.73 |
105C | 9.15 | 2.51 | 57.56 | 24.33 | 5.82 | 0.51 | 0.17 | 0.16 | 100.23 |
105C | 4.08 | 1.99 | 63.45 | 25.74 | 4.31 | 0.66 | 0.06 | 0.03 | 100.32 |
105C | 11.1 | 2.02 | 55.79 | 24.53 | 5.95 | 0.55 | 0.15 | 0.27 | 100.36 |
106A1 | 3.55 | 21.8 | 41.93 | 31.93 | 0.47 | 0.61 | 0.64 | 0.15 | 101.1 |
106A1 | 5.23 | 11.07 | 51.31 | 31.15 | 0.83 | 0.65 | 0.13 | 0.02 | 100.39 |
106A1 | 7.58 | 10.96 | 49.04 | 31.69 | 0.86 | 0.67 | 0.12 | 0.14 | 101.08 |
106A1 | 9.18 | 9.75 | 48.28 | 31.57 | 1.09 | 0.66 | 0.2 | 0.19 | 100.91 |
106A2 | 2.76 | 21.42 | 42.64 | 31.3 | 0.54 | 0.59 | 0.57 | 0.15 | 99.99 |
106A2 | 7.2 | 11.14 | 49.3 | 31.18 | 1 | 0.68 | 0.13 | 0.11 | 100.73 |
106A2 | 8.5 | 9.39 | 48.74 | 31.33 | 1.11 | 0.6 | 0.28 | 0.22 | 100.16 |
106A2 | 9.44 | 8.77 | 49.24 | 31.13 | 1.37 | 0.58 | 0.11 | 0.18 | 100.81 |
106B | 4.94 | 6.09 | 57.77 | 27.31 | 3.05 | 0.93 | 0.07 | 0.1 | 100.25 |
106B | 6.31 | 6.58 | 55.25 | 26.92 | 3.29 | 0.91 | 0.07 | 0.12 | 99.45 |
106B | 6.97 | 6.3 | 54.01 | 27.11 | 3.41 | 0.86 | 0.42 | 0.11 | 99.17 |
106B | 8.26 | 6.77 | 53.06 | 26.52 | 3.8 | 0.81 | 0.06 | 0.14 | 99.43 |
106C | 4.21 | 6.62 | 57.57 | 27.59 | 2.62 | 0.96 | 0.02 | 0.11 | 99.7 |
106C | 7.36 | 5.88 | 52.33 | 28.7 | 3.12 | 0.82 | 1.36 | 0.16 | 99.74 |
106C | 7.93 | 7.29 | 52.95 | 27.43 | 3.32 | 0.84 | 0.12 | 0.17 | 100.05 |
106C | 8.46 | 6.87 | 52.63 | 27.15 | 3.44 | 0.8 | 0.07 | 0.12 | 99.56 |
106D | 5.98 | 6.65 | 55.76 | 29.22 | 1.98 | 1.05 | 0.06 | 0.14 | 100.84 |
106D | 7.89 | 6.79 | 53.3 | 28.93 | 2.21 | 1.14 | 0.08 | 0.15 | 100.48 |
106D | 8.39 | 6.1 | 52.17 | 29.23 | 2.38 | 1 | 0.6 | 0.13 | 99.99 |
106D | 10.01 | 7.13 | 50.51 | 29.2 | 2.47 | 0.98 | 0.17 | 0.17 | 100.63 |
106E | 5.45 | 7.05 | 55.76 | 27.92 | 2.69 | 0.89 | 0.12 | 0.03 | 99.91 |
106E | 6.54 | 8.5 | 52.8 | 27.92 | 2.77 | 0.96 | 0.2 | 0.2 | 99.88 |
106E | 7.05 | 8.2 | 52.69 | 27.66 | 3 | 0.97 | 0.21 | 0.09 | 99.87 |
106E | 7.86 | 7.83 | 51.69 | 27.58 | 3.11 | 0.81 | 0.22 | 0.1 | 99.21 |
12 | 5.15 | 4.44 | 59.6 | 23.59 | 5.43 | 0.73 | 0.09 | 0.14 | 99.18 |
12 | 6.99 | 5.07 | 57.17 | 23.55 | 5.87 | 0.71 | 0.25 | 0.14 | 99.75 |
12 | 8.61 | 5.7 | 54.64 | 23.07 | 6.12 | 0.81 | 0.12 | 0.26 | 99.32 |
12 | 10.19 | 7.01 | 52.84 | 19.45 | 8.71 | 0.61 | 0.12 | 0.11 | 99.04 |
47A | 7.21 | 2.91 | 59.33 | 25.32 | 4.81 | 0.77 | 0.05 | 0.15 | 100.55 |
47A | 7.91 | 3.81 | 57.65 | 25.42 | 4.82 | 0.76 | 0.07 | 0.12 | 100.55 |
47A | 9.57 | 4.19 | 55.49 | 25.44 | 5.02 | 0.71 | 0.09 | 0.18 | 100.68 |
47A | 10.13 | 3.94 | 55.11 | 25.28 | 5.22 | 0.6 | 0.08 | 0.2 | 100.56 |
47B | 5.69 | 4.41 | 60.09 | 24.38 | 5.31 | 0.64 | 0.01 | 0.18 | 100.73 |
47B | 6.14 | 4.66 | 59.4 | 24.21 | 5.44 | 0.76 | 0.05 | 0.2 | 100.86 |
47B | 7.78 | 5.51 | 56.53 | 24.15 | 5.71 | 0.71 | 0.17 | 0.15 | 100.7 |
47B | 8.91 | 6.21 | 54.71 | 23.52 | 6.21 | 0.63 | 0.12 | 0.16 | 100.47 |
47C | 9.8 | 8.6 | 51.08 | 20.14 | 8.71 | 0.63 | 0.74 | 0.12 | 99.81 |
47C | 7.84 | 6.24 | 55.15 | 23.77 | 5.73 | 0.67 | 0.11 | 0.15 | 99.67 |
47C | 8.18 | 6.55 | 54.7 | 23.45 | 5.96 | 0.76 | 0.12 | 0.1 | 99.81 |
47C | 9.01 | 6.87 | 53.68 | 23.46 | 6.07 | 0.72 | 0.07 | 0.15 | 100.04 |
Sample CED | Mg | Nb | Cr | Al | W | Fe | Zr | V | T °C |
---|---|---|---|---|---|---|---|---|---|
D.L. | 30 | 110 | 45 | 30 | 135 | 30 | 55 | 30 | - |
47 | 80 | 150 | 23,100 | 230 | 550 | 560 | bd | 4530 | - |
47 | 110 | bd | 25,100 | 210 | 3900 | 580 | bd | 4570 | - |
47 | 50 | bd | 24,200 | 210 | 390 | 1040 | bd | 4520 | - |
106 | bd | 680 | 18,200 | 150 | 1180 | 850 | bd | 4320 | - |
106 | bd | 300 | 17,200 | 140 | 1410 | 790 | 170 | 4430 | 580 |
14 | 210 | bd | 8110 | 140 | 350 | 1440 | bd | 5060 | - |
14 | 70 | bd | 8940 | 210 | bd | 1370 | 60 | 4770 | 510 |
14 | 160 | bd | 7480 | 140 | bd | 1660 | bd | 5220 | - |
14 | bd | 140 | 9650 | 130 | 230 | 1490 | bd | 4910 | - |
105 | bd | 230 | 24,000 | 200 | 4180 | 580 | 90 | 4700 | 540 |
105 | 80 | 350 | 26,100 | 260 | 3120 | 540 | bd | 5000 | - |
105 | 100 | 490 | 26,300 | 250 | 3640 | 1030 | 70 | 4590 | 530 |
105 | 60 | 320 | 21,600 | 220 | 3360 | 430 | bd | 4730 | - |
105 | bd | 150 | 26,100 | 180 | 4340 | 770 | 60 | 4570 | 510 |
105 | 1330 | 170 | 24,300 | 240 | 5550 | 800 | 410 | 4700 | 650 |
105 | 70 | 360 | 23,700 | 210 | 6560 | 510 | bd | 5370 | - |
105 | 90 | 390 | 39,200 | 220 | 5090 | 1130 | 90 | 4700 | 540 |
105 | 40 | 380 | 25,400 | 180 | 6840 | 620 | 80 | 4850 | 530 |
105 | 50 | 420 | 33,500 | 220 | 6570 | 1480 | bd | 4470 | - |
100 | 40 | 650 | 14,300 | 150 | 870 | 860 | 430 | 5160 | 650 |
100 | bd | 1220 | 14,700 | 140 | 1080 | 1160 | 70 | 4740 | 520 |
100 | 40 | 900 | 14,100 | 200 | 470 | 1280 | 260 | 5240 | 610 |
100 | 30 | 4090 | 15,400 | 130 | 1140 | 640 | bd | 5080 | - |
100 | bd | 440 | 15,100 | 170 | 2970 | 780 | 540 | 4710 | 670 |
100 | bd | 560 | 12,800 | 180 | 630 | 750 | 60 | 4730 | 510 |
Sample CED | SiO2 | ZrO2 | Al2O3 | FeO | Cr2O3 | TiO2 | HfO2 | Y2O3 | Nb2O5 | UO2 | ThO2 | Ce2O3 | La2O3 | Nd2O3 | Pr2O3 | Total |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
105C | 34.09 | 63.36 | 0.3 | 0.54 | 0.81 | 0.07 | 0.9 | 0.33 | 0 | 0.07 | 0 | 0.08 | 0 | 0.27 | 0 | 100.81 |
105C | 33.62 | 62.26 | 0.5 | 0.63 | 0.31 | 0.11 | 1.29 | 0.24 | 0.04 | 0.11 | 0.11 | 0.09 | 0.03 | 0.79 | 0.06 | 100.19 |
105C | 33.69 | 62.84 | 0.63 | 0.75 | 0.41 | 0.11 | 0.92 | 0.38 | 0.06 | 0.11 | 0.13 | 0.18 | 0.07 | 1.18 | 0.02 | 101.47 |
105C | 33.82 | 63.45 | 0.22 | 0.45 | 0.59 | 0.07 | 0.83 | 0.64 | 0.04 | 0.14 | 0.03 | 0.08 | 0.07 | 0.14 | 0 | 100.57 |
105C | 34.01 | 63.51 | 0.18 | 0.37 | 0.62 | 0.1 | 0.89 | 0.35 | 0.05 | 0.09 | 0.02 | 0.03 | 0 | 0 | 0.08 | 100.3 |
105C | 32.42 | 62.41 | 0.95 | 0.7 | 0.43 | 0.15 | 1.17 | 0.26 | 0.02 | 0.18 | 0.19 | 0.07 | 0 | 0.88 | 0 | 99.84 |
105C | 32.11 | 63.4 | 0.54 | 0.56 | 0.51 | 0.1 | 1.23 | 0.16 | 0.02 | 0.12 | 0.08 | 0 | 0 | 0 | 0 | 98.83 |
Au3Pd | Au3Cu3Ni | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Sample | 105C | 106D | 106D | 47A | 47A | 47A | 47A | 47A | 47A | 47A | 47A |
wt % | |||||||||||
Pd | 14.15 | 14.55 | 13.81 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Au | 80.18 | 81.57 | 79.27 | 65.44 | 67.33 | 68.34 | 68.29 | 69.14 | 65.92 | 69.94 | 63.38 |
Cu | n.a. | n.a. | n.a. | 22.5 | 21.75 | 24.75 | 22.8 | 22.67 | 25.41 | 23.36 | 24.16 |
Ni | n.a. | n.a. | n.a. | 6.78 | 6.59 | 7.29 | 6.69 | 6.64 | 7.78 | 6.85 | 7.36 |
Total | 94.33 | 96.12 | 93.09 | 94.71 | 95.68 | 100.38 | 97.78 | 98.44 | 99.12 | 100.14 | 94.9 |
at % | |||||||||||
Pd | 24.59 | 24.81 | 24.37 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Au | 75.41 | 75.19 | 75.63 | 41.48 | 42.95 | 40.35 | 42.35 | 42.8 | 38.63 | 42.34 | 38.92 |
Cu | n.a. | n.a. | n.a. | 44.13 | 42.95 | 45.24 | 43.75 | 43.43 | 46.09 | 43.77 | 45.92 |
Ni | n.a. | n.a. | n.a. | 14.4 | 14.1 | 14.42 | 13.9 | 13.77 | 15.28 | 13.89 | 15.16 |
apfu | |||||||||||
Pd | 0.98 | 0.99 | 0.97 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Au | 3.02 | 3.01 | 3.03 | 2.9 | 3.01 | 2.82 | 2.96 | 3 | 2.7 | 2.96 | 2.72 |
Cu | n.a. | n.a. | n.a. | 3.09 | 3.01 | 3.17 | 3.06 | 3.04 | 3.23 | 3.06 | 3.21 |
Ni | n.a. | n.a. | n.a. | 1.01 | 0.99 | 1.01 | 0.97 | 0.96 | 1.07 | 0.97 | 1.06 |
© 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).
Share and Cite
Portella, Y.D.M.; Zaccarini, F.; Luvizotto, G.L.; Garuti, G.; Bakker, R.J.; Angeli, N.; Thalhammer, O. The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle. Minerals 2016, 6, 91. https://doi.org/10.3390/min6030091
Portella YDM, Zaccarini F, Luvizotto GL, Garuti G, Bakker RJ, Angeli N, Thalhammer O. The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle. Minerals. 2016; 6(3):91. https://doi.org/10.3390/min6030091
Chicago/Turabian StylePortella, Yuri De Melo, Federica Zaccarini, George L. Luvizotto, Giorgio Garuti, Ronald J. Bakker, Nelson Angeli, and Oskar Thalhammer. 2016. "The Cedrolina Chromitite, Goiás State, Brazil: A Metamorphic Puzzle" Minerals 6, no. 3: 91. https://doi.org/10.3390/min6030091