| 其他摘要 | The southwestern Guizhou Province is the most important metallogenic province of Carlin-type gold deposits in China. There are two kinds of Carlin-type gold deposits: fault-controlled and stratabound. The fault-controlled Carlin-type gold deposits are localized at the compressive shear faults and hosted in siltstones and silty mudstones of Middle or Lower Triassic. The stratabound Carlin-type gold deposits are controlled by anticlines and hosted in silty bioclastic limstones of Upper Permian. There are lots of studies on fault-controlled gold deposits, but a few on stratabound deposits. Recently, the new findings of some large scale stratabound gold deposits with high grade orebodies and ores make stratabound gold deposits as an important and characteristic kind of Carlin-type gold deposits in the area. The Shuiyindong gold deposit, the most important stratabound Carlin-type gold deposit, has been studied systematically, and the major understandings on its characteristics and model for it are as follows: 1. The gold deposit is controlled by both the structure and favorable lithology. It was located nearby the core of the Huijiabao anticline and orebodies are hosted in the limestone within the sedimentary series of clayrock-*-limestone-" clay rock. Most of orebodies are stratiform ones. However, some orebodies with less importance are controlled by low angle faults and called as fault-controlled orebodies. 2. The gold mineralization occurred under low-temperature with Th of 220°C±. Common hydrothermal alteration types such as silicification, dolomitization, and pyritization have been observed. The gold deposit has characteristic elemental assemblages of Au-As-Hg-Tl. Gold mainly presents as native gold, as tiny inclusions in As-rich pyrite rims on earlier stage pyrites and arsenopyrites. The As-rich pyrites and arsenopyrites are also very small (about several tens of fi m), which indicates that gold deposition might be due to quick change of metallogenetic conditions. 3. Fluid inclusions in vein quartz from the gold deposit are rich CO2, CH4, N2, (VCTI4+N2ICO2 inclusions have CH4 of 63 mo!e%, N?. of 18 mole%, CO2 of 19 mole%, respectively.), Th of 220°Ci , salinities of 6 wt.% ±, and minimum pressures of 1.6 ± 0.4 khar., indicating that the fluid is a overpressured one. The overpressured fluid is favorable factor for gold mineralzation, 4. Studies of geochemistry and isotope compositions indicate that the ore-bearing materials and fluids of the gold deposit mainly originated from plutonic source, and possess a mixing features with the strata matter during transportation from mantle to crust. The host rocks are common sedimentary rocks, and no evidence has been found for (hat there are some significant strata(ore-source bed), as well as for that ore-bearing materials originated from host strata. 5. The activity and heat-state of Earth's crust in long period are favorable for the formation of overpressured fluids in a large area, and extensive structures drove the fluids into ore-forming system and made gold deposits formed. The complexity of structural movement in upper crust of southwestern Guizhou, resulted in a complicated gold mineralzations. Unlike Nevada in western USA., there is a "Gold Triangle", but still no world-class Carlin-type gold deposits has been found in southwestern Guizhou. |
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