陕西镇安丘岭微细浸染型金矿床成矿物理化学条件及成矿机制研究

STUDY ON METALLOGENIC PHYSICOCHEMICAL CONDITIONS AND METALLOGENIC MECHANISMIOF THE QIULING MICRO-DISSEMINATED GOLD DEPOSIT IN ZHEN'AN COUNTY,SHAANXI PROVINCE

丘岭金矿床是产于南羊山组（Ｄ３ｎ）及袁家沟组（Ｃｙ）碳酸盐岩和细碎屑岩互层段中的微细浸染型金矿床。包裹体研究和热力学计算表明，成矿温度为１８４～３００℃，压力为４３０×１０５～３７５×１０５Ｐａ，形成深度＞１．５ｋｍ；成矿流体具弱酸－弱碱性、还原－弱还原性。矿源层中金以疏氢络合物Ａｕ（ＨＳ）＿２￣－及杂多核络合物Ｈ２Ａｕ（Ｓｂ，ＡＳ）Ｓ＿２￣０和ＨＡｕ（Ｓｂ，ＡＳ）Ｓ＿３￣－形式活化迁移，并在扩容减压带中沉淀富集。温度、压力降低，尤其是溶液中总硫活度的减小是矿质沉淀的重要因素。

Qiuling is a micro-disseminated (Carlin type )one which is hosted by carbonate rock and fine derital rock of Nanyanshan group and Yuanjiagou group.Fluid inclusion studies and thermodynamic calculations indicate that temperatures for ore deposition were from 151℃～300℃,pressures from 430×10-5Pa to 375×10-5Pa,and depth in excess of 1.5km.Oreforming solutions were weakly acid to weakly basic, reductive to weakly redctive .The gold in source bed was mobilized and migrated in the form Au(HS)2、H2Au(Sb,As)S and HAu(Sb ,As)S. When the ore-forming fluid converged into the low pressure zone,native gold was depoisited. A decrease in reduced sulfur activity by deposition of sulfides in hydrothermal ore fluids and a decline in temperature and pressure were the effective mechanism responsible for gold deposition.