新疆巴里坤小加山钨矿地质特征与成因

小加山钨矿区位于东准噶尔成矿区中部南缘,处于博格达-哈尔里克构造带上。构造位置上矿区处于哈尔里克复式背斜中,构造线方向以EW向为主。矿区出露地层主要为中泥盆统大南湖组第一亚组第一段(D_2d_1~1)、和第二段(D_2d_1~2)。主要岩浆岩有石英闪长岩、黑云母二长花岗岩、钾长花岗岩及少量中酸性花岗闪长岩脉。矿体赋存于邻近海西晚期花岗岩侵入体附近的中泥盆统大南湖组第一亚组第二段(D_2d_1~2)的变质晶屑凝灰岩中。矿石类型为石英脉型黑钨矿石,有用金属主要为黑钨矿,黑钨矿石英脉分为灰色含钨石英脉和白色含钨石英脉2种。四极质谱分析法测得矿床流体包裹体气相成分以H_2O、CO_2为主,次为N_2、CH_4,此外还含有少量的Ar、C_2H_6,液相成分以Cl~-、Na~+为主,次为Ca~(2+),表明成矿流体主要为H_2O-CO_2-NaCl体系。矿床成因类型属于高温热液石英脉型黑钨矿床,矿体主要位于围岩裂隙构造。钨主要由侵入围岩地层中的地幔热液迁移富集而来,W元素迁移过程中,含钨络合物成矿流体分解进而沉淀成矿。

Geological characteristics and genetic mechanism of the Xiaojiashan tungsten deposit in the Barkol district, Xinjiang

The Xiaojiashan tungsten deposit, located at the southern edge of the central area of east Junggar, is one of the metallic deposits in Bogda-Harlik tectonic belt. The structural position of the deposit is in the Harlik double anticline and the tectonic line is mainly EW-striking. The regional strata are mainly composed of 1st and 2nd lithologic member of the 1st Subformation of Middle Devonian Dananhu Formation (D₂d₁¹, D₂d₁²). The mining area has sporadic quartz diorite, moyite and a small number of intermediate-acid granodiorite veins. The orebodies occur in a late Hercian granite intrusion near the metamorphic crystal tuff which consists of the 2nd lithologic member of the 1st Dananhu Subgroup in Middle Devonian (D₂d₁²), whose type is wolframite ores of quartz vein, and wolframite is the main useful metal. Tungsten-bearing quartz veins are divided into gray wolframite-quartz vein and white quartz vein. Quadrupole mass spectrometry reveals that fluid inclusions contain major gas phase contents of CO₂, H₂O and a little variable positive ion component of Ca²⁺. In addition, there is a little variable components of Ar, C₂H₆ in gas phase. Meanwhile, fluid inclusions contain major liquid phase contents of Cl^-, Na⁺ and a little variable positive ion component of Ca²⁺. It can be inferred that the ore-forming fluid of the Xiaojiashan wolframite deposit is characterized by a CO₂-rich, low salinity, and H₂O-CO₂-NaCl system. The origin of the Xiaojiashan wolframite deposit can be considered as a high-temperature hydrothermal quartz vein type deposit controlled by fissure structures. Wolframite-bearing ore veins are distributed mainly over fissure structures. A portion of tungsten must have been sourced from migration and enrichment of mantle hydrothermal intrusion in wall rock and strata. Therefore, W-bearing complexes ore-forming fluid decomposed in the migration process of W, and promoted the precipitation of W in the Xiaojiashan deposit.