黑龙江省呼玛县天望台山金矿床成矿流体特征与成矿机制研究

Ore-forming fluid and metallogenic mechanism of Tianwangtaishan gold deposit, Heilongjiang Province

黑龙江省呼玛县天望台山金矿床位于大兴安岭北段,古利库-呼玛火山断陷盆地边缘的天望台山火山机构北部。文章将该矿床热液成矿期划分为4个成矿阶段:(Ⅰ)石英-黄铁矿阶段;(Ⅱ)石英-金-多金属硫化物阶段;(Ⅲ)石英阶段;(Ⅳ)方解石阶段。其中,第Ⅱ阶段为主成矿阶段。该矿床流体包裹体相态类型主要为富液两相型和富气两相型,另有少量纯液相型和纯气相型。各阶段成矿流体的均一温度峰值区间为:280~320℃→240~280℃→220~260℃→200~240℃,成矿流体具有中低温的特点,其盐度、压力、密度和成矿深度显示出浅成低温热液型矿床的特点。主成矿阶段流体气相成分主要为H2O、CO2、N2和O2,液相中离子成分主要有Na+、K+、Ca2+和SO2-4、Cl-。主成矿阶段流体的δDV-SMOW范围为-163.5‰^-131.9‰,δ18OV-SMOW范围为-11.2‰^-9.1‰,反映成矿流体为大量大气降水和少量岩浆水的混合。主成矿阶段强烈的降温降压作用可能是导致成矿元素沉淀成矿的主要机制。此外,本次的流体包裹体研究结果表明该矿床的成矿流体在主成矿阶段发生过流体不混溶作用。因此,本文认为成矿流体强烈的降温降压作用,以及伴随着的流体不混溶是天望台山金矿床的成矿机制。

The Tianwangtaishan gold deposit is located in the northern segment of Tianwangtaishan volcanic edifice on the margin of Guliku-Huma volcano-graben basin, and lies in North Da Hinggan Mountains. Four ore-forming stages have been recognized, i. e., quartz-pyrite stage（ Ⅰ）, quartz- gold-polymetallic sulfide stage（ Ⅱ）, quartz stage（ Ⅲ）, and quartz-calcite stage（ Ⅳ）. And the metallogenesis mainly occurred in stage（ Ⅱ）. A large number of liquid-rich two-phase type and gas-rich two-phase type fluid inclusions, together with a few pure liquid single-phase type and pure gas single phase type fluid inclusions, dominated all mineralization stages. Homogenization temperatures of fluid inclusions in four stages are concentrated on 280 - 320℃ →240 - 280℃ →220 - 260℃ →200 -240℃, which demonstrates that the ore-forming fluid had intermediate-low temperature characteristics. The salinities and pressures of ore-forming fluids and the metallogenic depth show the same features as the epithermal deposit. The gaseous content of mass fluid inclusions is mainly composed of H2 O, CO2,N2 and O2, while aqueous components mainly contain Na^＋, K^＋, Ca^2＋and SO4^2-, Cl^-. δDV-SMOWof the fluid is between- 163. 5‰ and-131. 9‰,whereas δ18OV-SMOWof the fluid is between- 11. 2‰ and- 9. 1‰, which suggests that the source of oreforming fluid was made up of a large amount of meteoric fluids with lesser amounts of magmatic fluids. The intense cooling and depressurization during the main stage was the most important reason for the precipitation of metallogenic elements. In addition, a study of fluid inclusion assemblages in stage（ Ⅱ） suggests that immiscibility occurred during the main ore-forming stage. It is thus held that the intense cooling and depressurization of ore-forming fluid,associated with its immiscibility, are the main metallogenic mechanisms of this gold deposit.