新疆富蕴县蒙库铁矿地质地球化学特征

Geology and geochemistry of the Mengku iron deposit,Fuyun County,Xinjiang.

蒙库是新疆境内目前发现的最大的磁铁矿矿床,矿体赋存在下泥盆统康布铁堡组角闪变粒岩、斜长角闪岩(原岩为火山岩)中。探明铁储量1.1亿吨,全铁平均品位44%。矽卡岩广泛发育并与矿体关系密切,矽卡岩阶段主要发育钙铁榴石、透辉石等矿物,晚期矽卡岩阶段则以大量阳起石、绿泥石、透辉石并伴随磁铁矿的出现为特征。矽卡岩阶段石榴石中原生包裹体类型复杂,均一温度为348℃～500℃,盐度为9.6～12.85wt%;晚期矽卡岩阶段透辉石中富液包裹体的均一温度为241℃～490℃.盐度为10.73～12.96wt%;含子晶的石英包裹体均一温度为348℃～458℃,盐度为38.2～57.1 wt%,石英气液包裹体的均一温度在166℃～382℃之间,盐度为9.6～13.04wt%,平均11.31wt %;方解石中富液包裹体的均一温度为145℃～265℃,盐度1.23%～9.6%,流体表现为矽卡岩化过程的中高温中等盐度到中温中等盐度流体再到低温低盐度的演化历程。δ^(34)S的值显示硫的来源于均一的硫的储库,有少量地层硫加入。碳、氢、氧同位素组分表明交代火山岩的流体主要为岩浆晚期的热水溶液。在演化的晚期有大气降水的加入。

The Mengku skarn deposit is the largest magnetite deposit in Xinjiang. The orebodies are hosted by amphibole fined-grained gneiss and amphibolite ( the protoliths are volcanic rocks) in the Lower Devonian Kangbutiebao Formation. This deposit has identified iron reserves of 110 million tons with a average total iron grade of 44%. Skarn is widespread and closely related to the orebodies. The skarn stage mainly witnessed the development of such minerals as andradite and diopside, and the late skarn stage was characterized by the appearance of abundant actinote, chlorite and diopside, accompanied by the appearance of magnetite. The types of primary fluid inclusions in garnet of the skarn stage are complex, with homogenization temperatures of 348 to 500 degrees C and corresponding salinities of 9. 6 to 12. 85 wt. % NaCl equivalent. Homogenization temperatures of liquid-rich inclusions in diopside associated with the late skarn stage range from 241 to 490 degrees C and their salinities vary from 10. 73 to 12. 96 wt. % NaCl equivalent. Homogenization temperatures for quartz inclusions containing daughter crystals range from 348 to 458 degrees C and their corresponding salinities range from 38. 2 to 57. 1 wt. % NaCl equivalent. Homogenization temperatures for two-phase inclusions in quartz vary from 166 to 382 degrees C and their salinities are 9. 6 to 13. 04 wt. % NaCl equivalent with an average of 11. 31 wt% NaCl equivalent. Homogenization temperatures of liquid-rich inclusions in calcite vary form 145 to 265 degrees C, with a salinity of 1. 23 to 9. 6 wt. % NaCl equivalent. Fluids evolved from high- and moderate-temperature and moderate-salinity fluids through moderate-temperature and moderate-salinity fluids to low-temperature and low-salinity fluids. delta S-34 values indicate that sulfur was mainly derived from the homogenous mantle reservoir, but some sulfur from strata was introduced at the late stage. Carbon, hydrogen and oxygen isotope components show that the fluids replacing volcanic rocks were mainly late magmatic hydrothermal solutions and that meteoric water was introduced in the hydrothermal solutions in the late stage of the evolution.