黔西南卡务金矿热液方解石地球化学特征及其找矿意义OA

The Southwest Guizhou region has the largest concentration of Carlin-type gold deposits in China.The Kawu gold deposit is one example of this,with well-developed calcite veins within the mining area.The classification of calcite veins of different ages and determination of calcite veins closely related to mineralization have long been major challenges in the exploration work at the Kawu gold deposit.In this study,calcite veins were collected in different tectonic zones of the Kawu gold deposit on the basis of detailed field investigations,and calcite cathodoluminescence and in situ LA-ICP-MS analyses were performed to reveal the tectonic zones in which calcite is present during mineralization and the geochemical characteristics of the mineralizing fluids,thereby providing a basis for mineral exploration in the mining area.Calcite veins of syntectonic origin were collected from typical structural locations within the research area;namely,the upper plate of the regional fault,joint and fracture fillings within the mining area,and the core of the regional fold.The veins were successively classified into three generations according to the cross-cutting relationships observed in the field.The first-generation veins,which were present in the upper plate of the regional fault,had the highest average sum of rare earth elements(ΣREE=74.824 μg/g)among the three generations,with LREE/HREE=0.976,indicating the weakest degree of fractionation.The(La/Yb)N ratio was 1.86,indicating a relatively flat chondrite-normalized REE pattern.No Ce anomaly(δCe=0.92)and a weak negative Eu anomaly(δEu=0.763)were found in these veins.The second-generation veins,found in extensional fractures within the mining area,showed a significant decrease in the average ΣREE(4.674 μg/g)compared with that of the first generation.The LREE/HREE ratio was 0.19,indicating significant MREE enrichment.The(La/Yb)N ratio was 0.261 for these veins,and they displayed a hump-shaped REE pattern,weak negative Ce anomaly(δCe=0.76),and weak positive Eu anomaly(δEu=1.339).The third-generation veins,located in the core of the regional fold and in secondary structures in the lower plate of the regional fault,had an average ΣREE value(4.591 μg/g)similar to that of the second-generation veins.The LREE/HREE ratio was 4.39,indicating significant LREE enrichment and a relative depletion of HREE.The(La/Yb)N ratio was 16.7 for these veins,and they showed a right-leaning REE pattern,no Ce anomaly(δCe=0.918),and a strong positive Eu anomaly(δEu=5.915).The Eu anomaly changes in the three generations indicate that the first generation existed in a moderately low-temperature and slightly oxidizing environment,which changed to a moderately low-temperature and slightly reducing environment in the second generation and then to a higher-temperature and more reducing environment in the third generation.According to the REE geochemical characteristics of the calcite veins,those filling the fractures in extensional spaces in the mining area closely resembled calcite veins from the mineralization stage of Carlin-type gold deposits in the region,indicating they are in the mineralization period;those found in the hanging wall of the regional fault were classified as being in the pre-mineralization period;whereas those that developed in the core of regional folds and within secondary structures in the footwall of the regional fault were in the post-mineralization period.This indicates that mineralization of the Kawu gold deposit lagged behind the tectonic deformation process,with mineralizing fluids filling the extensional spaces created by tectonic deformation.Future exploration efforts should focus on the extensional spaces generated by tectonic deformation in the mining area.