U-Pb age and lead isotopic characterization of Au-bearing skarn related to the Andorra granite (central Pyrenees, Spain)

AbstractThe Dachang gold deposit is located in the Late Triassic Songpan-Ganzi Fold Belt, NE Tibetan Plateau. Gold ore is concentrated as veins along secondary faults and fracture zones in the Bayan Har Group metaturbidites. No exposed felsic plutons are present in the vicinity of the deposit. The auriferous veins contain <15% sulphide minerals, mainly arsenopyrite, pyrite, and stibnite. Gold is commonly enclosed within arsenopyrite and pyrite. Typical alteration around the ore bodies includes silicification, sericitization, and weak carbonatization.Gold-bearing quartz samples have δ18O values of 16.9–21.2‰ (V-SMOW) from which δ18OH2O values of 6.2–9.6‰ can be calculated from the fluid inclusion temperatures (or 10.0 to 12.7‰ if we used the average arsenopyrite geothermometer temperature of 301°C). The δD values of fluid inclusions in quartz range from –90‰ to –72‰. δ34S values of gold-bearing sulphides mainly range from –5.9‰ to –2.8‰ (V-CDT). Pyrite and arsenopyrite in ores have 206Pb/204Pb ratios of 18.2888 to 18.4702, 207Pb/204Pb ratios of 15.5763 to 15.6712, and 208Pb/204Pb ratios of 38.2298 to 38.8212. These isotopic compositions indicate that the ore-forming fluids were of metamorphic origin, and the S and Pb may have been derived from the host metaturbidites of the Bayan Har Group. The Dachang Au deposit has geological and geochemical features similar to orogenic gold deposits. We propose that the ores formed when the Songpan-Ganzi Fold Belt was intensely deformed by Late Triassic folding and thrusting. Large-scale thrusting resulted in regional allochthons of different scales, followed by secondary faults or fracture zones that controlled the ore bodies.Keywords: orogenic gold depositO–H–S–Pb isotopesDachang gold depositSongpan-Ganzi Fold BeltNE Tibetan Plateau AcknowledgementsThis work was granted by China Natural Sciences Foundation (Grant No. 40802021), Postdoctoral Research Grant of Nanjing University, and Basic Scientific Research Foundation of Jilin University (Grant No. 421030454422). Thanks are also due to the Fifth Geological Prospecting Institute in Qinghai Province, Qinghai Geology Survey, China, and Inter-Citic Mineral Inc., Canada. We also want to thank Drs Shijin Li, Junwei Zhao, and Tong Pan for their assistance during field works. The comments and English corrections by Prof. Frimmel considerably improved the manuscript and are gratefully acknowledged.

Arsenopyrite

δ34S

Magmatic water

Ore genesis

10.1080/00206814.2013.804687

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Citations (15)

Micrometallogeny and hydrothermal fluid evolution of the Iju porphyry Cu deposit, NW Kerman, Iran: Evidence from fluid inclusions, Laser Raman spectroscopy, and S O isotope systematics

Geochemistry (2023)

E. Mahmoudi Sina Asadi Shahla Sharifpour

δ34S

Magmatic water

Mineral redox buffer

10.1016/j.chemer.2023.125956

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Citations (1)

Source of Fluids in the Auriferous El Cabaco Mineralized Zone, Southern Salamanca

International Geology Review (1994)

J. F. Antona Anthony E. Fallick Antonio García Sánchez

This paper assesses chemical-mineralogical changes resulting from hydrothermal alteration associated with granite-hosted gold mineralization in southern Salamanca province, Spain. Within the mineralized veins, along planes of quartz growth, two types of fluid inclusions were observed. One type is rich in CH4 with minor CO2, the other is rich in H2O with CO2 (± CH4). These are interpreted as reflecting the immiscibility of an initial fluid rich in H2O-CH4 and some CO2. Inclusions with similar composition are seen at the silicification formed at the granite contact with host rocks. However, differences in P-T conditions and immiscibility of fluids are indicated by the microthermometric study and relation of the inclusions. These are consistent with the temperatures calculated from the arsenopyrite-pyrite geothermometer. Formation temperatures of 445 ± 15° C were deduced for the mineralization at the granite contact and temperatures not exceeding 386° C for the vein mineralization. Metasomatically altered granites are depleted in Na and K in comparison to fresh granites. A gain in CO2 has been measured in the altered rocks. No correlation was found between gold contents and any of the major or trace elements analyzed. δ34S arsenopyrite values suggest a variable source of sulfur. Calculated δDfluid values show significant variability (−66 to −37%0 SMOW), whereas δ18O fluid values show small variation (from +7.6 to +8.4%o SMOW). These values for the fluids are consistent with interaction between magmatic fluids and metamorphic rocks. Gold deposition in quartz veins could be explained by the loss of H2S during fluid immiscibility.

Arsenopyrite

δ34S

Wolframite

10.1080/00206819409465482

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Citations (2)