| Ganzi-Litang gold belt is located in the Eastern Qinghai-Tibet Plateau, the junction area of Songpan-Ganzi orogenic zones and Yidun arc orogen. The gold belt is an important gold-copper polymetallic ore belt, have discovered many medium-sized gold districts recent years, showing vast resources potential and exploration prospects.The authors attempt to explore the ore-formating temperature, depth and environments of the six gold deposits, i.e. Gala gold ore district, Cuoa gold ore district, Xichongnong gold ore district, Xionglongxi gold ore district, Ajialongwa gold ore district and Qukailongwa gold ore district, using electron microprobe analysis of the main gold-bearing minerals pyrite and arsenopyrite, and Quartz, ankerite, sericite, etc. Combination of apatite and zircon fission track dating of ores and host rocks in the gold belt, we discussed the mineralization age and the laws of the times, and did a simulation of thermal history to reveal the magmatic tectonic activity effects on mineralization.Through the electron microprobe analysis and the symbiotic relationship between minerals, with the previous studies and fluid inclusion test results, we concluded that the Ganzi-Litang gold deposits formed in a high oxygen fugacity, low-temperaturehydrothermal environment, and the mineralization is related to alkaline Magmatic hydrothermal, the forming temperature is about 165 ~ 250℃. And the gold deposits formed in middle-shallow depths and middle-low temperature hydrotherm, and there are also deep and shallow output features,that’s to say, the formation of gold there are multiple periods, with the characteristics of different depths.Based on apatite and zircon fission track analysis, we concluded that the gold mineralization is mainly between 80~140Ma, the main mineralization is in Cretaceous with multi-stage features, from south to north, the mineralization changes smaller. In northern section the ore age of Gala gold ore district is 82±5Ma, the ore age of Xionglongxi gold ore district in middle section is 107±7Ma, and in the Southern Section, Ajialongwa gold ore district is 140±8Ma, while Qukailongwa gold ore district is 124±7Ma and 130±7Ma.The zircon fission track dating and apatite fission track the results showed that the cooling speed from south to north is changing faster.From the zircon closure temperature 250℃to the apatite closure temperature 100℃, the average rate is 1.46℃/Ma, 1.67℃/Ma and 2.21℃/Ma. From 100℃fell to the surface temperature (15℃), the rate is 3.15℃/Ma, 5℃/Ma and 6.07℃/Ma, corresponding uplift rate is 104.9m/Ma, 166.7m/Ma and 202.4m/Ma. And the cooling and uplift rate of northern section was faster than the southern section.The apatite fission track simulation results show that over the past 30Ma, region cooled faster, on average 4℃/Ma, and especially since the recent 3Ma, the region uplifted in a very fast rate, the average is 20℃/ Ma, 667 m/Ma, it was a rapid uplift, about 2 km.Through research on thermal history of the gold ore and surrounding rocks in Ganzi-Litang gold belt, found that the gold belt all experienced two stable and two rapid cooling periods, late with the Yanshan and Himalayan tectonic magma corresponds. |
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