桂北都庞岭地区猫儿石锡多金属矿床流体特征与成矿机制研究

Fluid Characteristics and Metallogenic Mechanism of the Maoershi Tin Polymetallic Deposits in the Dupangling Area of Northern Guangxi

摘要: 桂北都庞岭地区位于北东向钦杭成矿带与东西向南岭成矿带的复合部位，区域内的锡多金属矿床尚未开展流体包裹体方面的分析测试工作，成矿机制一直未能准确限定。为精确刻画区域内锡多金属成矿作用过程，本文对猫儿石锡多金属矿床开展了流体包裹体显微测温和氢氧同位素分析。研究显示，流体包裹体类型较为简单，主要为富液两相包裹体和少量富气两相包裹体。从早到晚均一温度依次为281℃~415℃、231℃~280℃和154℃~230℃，对应盐度为4.63%~12.42% NaCleqv (平均9.69%)、3.21%~13.66% NaCleqv (平均9.24%)和2.06%~16.14% NaCleqv (平均8.71%)。富液两相包裹体气相和液相成分均为H₂O，富气两相包裹体流体成分除H₂O外，还含有少量CO₂、N₂、CH₄；δD_v-SMOW值为−55.1‰~−67.1‰；δ¹⁸ O_v-SMOW值为10.2‰~12.9‰，初步厘定初始成矿流体为贫CO₂的H₂O-NaCl体系的岩浆热液，成矿期逐渐向大气降水靠近。印支期岩浆结晶分异形成的富锡多金属流体沿断裂上升过程中，与大气降水混合，导致成矿物质卸载。因此，流体混合是猫儿石锡多金属矿床锡的主要成矿机制。

Abstract: The Dupangling area in northern Guangxi is situated within the composite section of the northeast Qinhang metallogenic belt and the east-west Nanling metallogenic belt. The analysis and testing of fluid inclusions in the Sn polymetallic deposits in this area have yet to be conducted, and the metallogenic mechanism remains to be accurately defined. In order to provide an accurate description of the mineralisation process of Sn polymetallic deposits in the region, this paper employed micro thermometry and hydrogen-oxygen isotope analysis of fluid inclusions in the Maoershi Sn polymetallic deposit. The study demonstrates that the types of fluid inclusions are relatively simple, comprising primarily liquid-rich two-phase inclusions and a minor quantity of gas-rich two-phase inclusions. The homogenisation temperatures ranged from 281˚C to 415˚C, 231˚C to 280˚C and 154˚C to 230˚C, with corresponding salinities of 4.63 to 12.42 wt% NaClequiv (average 9.69%), 3.21 to 13.66 wt% NaClequiv (average 9.24%) and 2.06 to 16.14 wt% NaClequiv (average 8.71%). The gas and liquid components of the liquid-rich two-phase inclusions are both constituted by H₂O. In addition to H₂O, the fluid components of the gas-rich two-phase inclusions also contain a small amount of carbon dioxide, nitrogen and methane. The δD value was found to be in the range of −55.1‰ to −67.1‰ VSMOW. The δ¹⁸O water values span a range of 10.2‰ to 12.9‰ VSMOW, indicative of an initial ore-forming fluid comprising CO₂-poor H₂O-NaCl magmatic hydrothermal components, with the ore-forming period gradually approaching meteoric water. The Sn-rich polymetallic fluid, formed by the crystallisation and differentiation of the Indosinian magma, rises along the fault and mixes with atmospheric precipitation, resulting in the unloading of ore-forming materials. It can thus be concluded that fluid mixing represents the primary metallogenic mechanism responsible for the occurrence of Sn in the Maoershi tin polymetallic deposit.