豫陕小秦岭脉状金矿床三期流体运移成矿作用

A three stage fluid flow model for Xiaoqinling lode gold metallogenesis in the He'nan and Shaanxi provinces, central China.

位于豫陕交界处的小秦岭脉状金矿是我国第二大黄金产出集中地。流体包裹体研究表明,脉状金矿床石英及碳酸盐矿物中流体包裹体主要有富CO_2包裹体、CO_2-H_2O包裹体和H_2O溶液包裹体等三种类型,各热液阶段形成的脉体内有不同的流体包裹体组合。脉状金矿体的形成经历了三期流体成矿作用,第一期形成乳白色石英大脉,它构成了矿脉的主体,流体的性质为富H_2O热液,但无金的成矿;第二期(成矿期)流体为中低盐度CO_2-H_2O-NaCl热液,它叠加在了石英大脉之上,形成(块状)黄铁矿-浅色石英矿体和(网脉状)多金属硫化物-烟灰色石英矿体,成矿期内热液的温度、压力及流体组成的变化是金沉淀成矿的原因;第三期热液又转成低盐度的富水流体,形成石英-碳酸盐脉体,金矿化微弱。

The Xiaoqinling lode gold field is located in the boundary of He'nan and Shaanxi provinces in central China. More than 1200 gold-bearing quartz veins have been found in the field and it is the second largest gold concentration region of China. All lode gold deposits possess similar mineral assemblages, deformational state, fluid flow characteristics, ore fluid composition and have comparable P - T conditions. Fluid inclusion studies show that large number fluid inclusions, including CO2-rich inclusions, CO2-H2O inclusions and aqueous inclusions, are hosted in vein quartz and carbonate in various mineralization stages. Three successive crystallisation stages are recorded during the formation of gold-bearing veins. Stage 1 - the development of milky quartz veins that formed main parts of the quartz veins. The fluids were H2O-rich and no clear evidence was found for gold deposition during this stage. Stage 2 - intense microfissuring of the earlier quartz vein (Stage 1) infillings occurred, associated with the main episode of gold deposition. Massive pyrite-clear quartz ores and network polymetallic sulfide minerals-grey colour quartz ores formed. The fluids were middle-low salinity CO2-H2O-NaCl type. Changes of temperature, pressure and fluid compositions in ore-forming fluids were main causes for gold deposition. Stage 3 fluids changed to lower salinity H2O-rich type. Quartz-carbonate mineral veins were formed and weak gold mineralization happened.