川西北马脑壳金矿床流体包裹体研究及对成矿条件的制约

Study of fluid inclusions and the constraint for ore-forming conditions of gold deposit at Manaoke, northwestern Sichuan province.

川西北的马脑壳金矿床为一赋存于三叠系碎屑岩、碳酸盐岩系的大型微细浸染型金矿床。通过详细野外地质调查和室内综合研究 ,可将矿床的热液成矿作用划分为四个阶段。应用均一法测得 : 、 、 、 阶段的成矿温度分别为 175～2 30℃ ,179～ 2 5 5℃ ,15 7～ 2 0 7℃ ,12 0～ 2 0 0℃ ;峰值分别为 190～ 2 10℃ ,2 0 0～ 2 30℃ ,170～ 190℃ ,130～ 170℃。盐度变化范围 , 、 、 阶段分别为 4.9～ 11.0 ,4.0～ 9.5 ,0 .85～ 5 .85 eq.wt% Na Cl。流体包裹体的气相组分以 H2 O和 CO2 为主 ,含有少量CO、CH4和 H2 ;液相组分以 HCO-、Ca2 +、K+、Na+和 Cl-为主 ,SO42 -、L i+、F-的含量较低。成矿热液的 p H值界于 6 .7～ 7.2 ,Eh为 - 0 .6 9～ - 0 .73。由此反映出 :成矿流体具有中低温 ,中低盐度 ,富含 H2 O、CO2 、HCO- 、Ca2 + 、K+ 、Na+ 、Cl- ,中性 ,弱还原的特点。从成矿作用早期至晚期 ,流体的总体演化趋势是温度逐渐降低 ,但在 阶段温度呈现出相反的变化 ,可能是在热液成矿作用过程中加入岩浆热液的结果 ;热液的盐度从早期到晚期逐渐下降 ;

Manaoke gold deposit situated in Northwestern Sichuan is hosted in mid Triassic detrital and carbonate rocks. Through the synthetical study in field and indoor, the hydrothermal mineralization can be subdivided into four stages. The homogenization temperatures of four stages are 175~230℃,179~255℃,157~207℃,120~200℃, respectively; population values are 190~210℃,200~230℃,170~190℃,130~170℃, respectively?The salinities of Ⅰ?Ⅱ?Ⅳ stages are 4.9~11.0,4.0~9.5,0.85~5.85 eq.wt%NaCl, respectively. The components of vapor phase are H 2O and CO 2 mainly, and the CO, CH 4, H 2 only a little, the components of liquid phase are HCO -, Ca 2+ , K +, Na +, and Cl - mainly, and the SO 4 2- , Li+, F - only a little. The pH of ore forming fluid is 6.7~7.2, and Eh -0.69^-0.73. From these data, it can be concluded that the characters of ore forming fluid are mid low temperature, low salinity, rich H 2O, CO 2, HCO -, Ca 2+ , K +, Na +, and Cl -, middle pH and weak reduction. From the early period to late period of hydrothermal mineralization the temperature becomes lower gradually in general; however, in stage II the temperature becomes higher, maybe this is the result of introduction of magma water occurred in the processes of mineralization. The salinity becomes lower from early to late period and the pH and Eh change a little in all processes of hydrothermal mineralization.