Genesis of the Koka Gold Deposit in Northwest Eritrea, NE Africa: Constraints from Fluid Inclusions and C–H–O–S Isotopes
Abstract
:1. Introduction
2. Regional Geology
3. Geology of the Koka Deposit
4. Sampling and Analytical Method
4.1. Fluid Inclusions (FIs)
4.2. Stable Isotope Analytical Methods
5. Fluid Inclusions
5.1. Fluid Inclusion Petrography
5.2. Fluid Inclusion Microthermometry
5.3. Laser Raman Spectroscopy
5.4. Ion and Gas Chromatography
6. C–H–O–S Isotopes
7. Discussion
7.1. Nature and Evolution of Ore-Forming Fluid
7.2. Source of Ore-Forming Fluids and Metal
7.3. Genetic Model for Ore Deposition
8. Conclusions
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
References
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Sample No. | Stage | FI type | Size (μm) | Number | Tm, CO2 (°C) | Tm, ice (°C) | Tm, Cl (°C) | Th, CO2 (°C) | Th, (°C) | Salinity (wt% NaCl) | Density (g/cm3) |
---|---|---|---|---|---|---|---|---|---|---|---|
KO-15 | Stage I | Type I, minor | 6~12 | 4 | –4.3~–2.4 | 254~341 (V) | 4.0~6.9 | 0.757~0.822 | |||
Type II, abundant | 8~16 | 9 | –56.9~–58.0 | –2.3~17.2 | 0.801~0.904 | ||||||
Type III, abundant | 8~16 | 11 | –56.7~–57.9 | 5.7~7.8 | 19.2~30.1 | 280~356 (V) | 4.3~7.9 | 0.576~0.793 | |||
KO-16 | Type I, minor | 6~12 | 5 | –2.6~–1.9 | 243~288 (V) | 3.2~4.3 | 0.711~0.831 | ||||
Type II, abundant | 6~12 | 10 | –56.7~–58.2 | –4.9~18.9 | 0.757~0.898 | ||||||
Type III, minor | 6~20 | 14 | –56.8~–58.1 | 5.8~7.9 | 19.9~29.6 | 235~295 (V) | 4.1~7.7 | 0.608~0.783 | |||
KO-17 | Type I, minor | 6~12 | 6 | –3.2~–1.8 | 223~275 (V) | 3.1~5.3 | 0.783~0.858 | ||||
Type II, abundant | 6~14 | 13 | –56.8~–58.0 | –4.7~16.4 | 0.812~0.901 | ||||||
Type III, abundant | 10~24 | 14 | –56.6~–58.0 | 5.3~8.0 | 10.6~29.4 | 238~305 (V) | 3.3~8.5 | 0.613~0.862 | |||
KO-3 | Stage II | Type I, abundant | 8~16 | 6 | –2.6~–1.5 | 221~288 (V) | 2.6~4.3 | 0.765~0.872 | |||
Type III, abundant | 8~20 | 11 | –57.0~–57.9 | 6.2~8.2 | 19.7~29.7 | 228~295 (V) | 3.5~7.1 | 0.613~0.787 | |||
KO-7 | Type I, abundant | 8~12 | 6 | –2.8~–1.3 | 212~280 (V) | 2.2~4.7 | 0.763~0.871 | ||||
Type III, abundant | 8~24 | 11 | –56.9~–57.4 | 6.6~8.5 | 18.5~29.7 | 232~318 (V) | 3.0~7.5 | 0.597~0.793 | |||
KO-14 | Type I, minor | 8~14 | 5 | –2.6~–0.9 | 235~267 (V) | 2.2~4.3 | 0.786~0.842 | ||||
Type III, abundant | 10~22 | 10 | –56.7~–57.3 | 5.6~8.0 | 18.2~25.7 | 259~309 (V) | 3.9~8.0 | 0.672~0.701 |
Sample No. | Stage | H2O | CO2 | CO | CH4 | K+ | Na+ | Ca2+ | Mg2+ | Cl− | SO42− |
---|---|---|---|---|---|---|---|---|---|---|---|
mol% | mol% | mol% | mol% | mg/L | mg/L | mg/L | mg/L | mg/L | mg/L | ||
KO-15 | Stage I | 0.595 | 0.405 | <0.01 | <0.01 | 0.18 | 4.74 | 0.09 | 0.02 | 5.99 | 0.52 |
KO-16 | 0.526 | 0.474 | <0.01 | 0.11 | 0.31 | 6.24 | 0.07 | <0.01 | 8.36 | 0.48 | |
KO-17 | 0.484 | 0.516 | <0.01 | <0.01 | <0.01 | 5.22 | 0.06 | <0.01 | 6.52 | 0.56 | |
KO-3 | Stage II | 0.741 | 0.259 | <0.01 | <0.01 | 0.47 | 8.06 | 0.08 | <0.01 | 9.62 | 0.50 |
KO-7 | 0.765 | 0.235 | <0.01 | <0.01 | 0.88 | 11.22 | 0.10 | 0.02 | 15.63 | 0.50 |
Sample NO. | Stage | Mineral | δDsmow (‰) | δ18Osmow (‰) | δ18OH2O (‰) | δ13Cv-PDB (‰) | Temperature (°C) |
---|---|---|---|---|---|---|---|
KO-15 | Stage I | Quartz | –52.5 | 9.7 | 2.4 | –5.0 | 290 |
KO-16 | Quartz | –57.0 | 9.0 | 1.7 | –5.4 | 290 | |
KO-17 | Quartz | –50.1 | 9.5 | 2.2 | –5.5 | 290 | |
KO-3 | Stage II | Quartz | –53.1 | 10.8 | 2.7 | –4.4 | 270 |
KO-7 | Quartz | –54.1 | 10.1 | 2.0 | –4.4 | 270 |
Sample No. | Stage | Mineral | δ34SCDT (‰) |
---|---|---|---|
KO-11 | Stage I | Pyrite | 1.7 |
KO-11 | Pyrite | −0.1 | |
KO-15 | Pyrite | 1.3 | |
KO-16 | Pyrite | 1.4 | |
KO-17 | Pyrite | 1.6 | |
KO-17 | Pyrite | 1.6 | |
KO-17 | Chalcopyrite | 1.3 | |
KO-17 | Galena | –1.3 | |
KO-17 | Sphalerite | 1.2 | |
KO-3 | Stage II | Pyrite | 1.9 |
KO-3 | Pyrite | 1.9 | |
KO-7 | Pyrite | 2.7 | |
KO-14 | Pyrite | 1.8 |
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Zhao, K.; Yao, H.; Wang, J.; Ghebretnsae, G.F.; Xiang, W.; Xiong, Y.-Q. Genesis of the Koka Gold Deposit in Northwest Eritrea, NE Africa: Constraints from Fluid Inclusions and C–H–O–S Isotopes. Minerals 2019, 9, 201. https://doi.org/10.3390/min9040201
Zhao K, Yao H, Wang J, Ghebretnsae GF, Xiang W, Xiong Y-Q. Genesis of the Koka Gold Deposit in Northwest Eritrea, NE Africa: Constraints from Fluid Inclusions and C–H–O–S Isotopes. Minerals. 2019; 9(4):201. https://doi.org/10.3390/min9040201
Chicago/Turabian StyleZhao, Kai, Huazhou Yao, Jianxiong Wang, Ghebsha Fitwi Ghebretnsae, Wenshuai Xiang, and Yi-Qu Xiong. 2019. "Genesis of the Koka Gold Deposit in Northwest Eritrea, NE Africa: Constraints from Fluid Inclusions and C–H–O–S Isotopes" Minerals 9, no. 4: 201. https://doi.org/10.3390/min9040201