青海祁漫塔格地区矽卡岩型矿床花岗质岩石矿物学及地质意义

青海祁漫塔格地区位于东昆仑造山带西段,是我国近些年来的重点找矿地区之一。本文对区内与虎头崖矿床I矿带(Fe)、野马泉矿床(Fe)、虎头崖矿床VI矿带(Zn)和卡而却卡矿床B区(Cu)有关的花岗质岩石开展了矿物学研究。结果显示,虎头崖矿床I矿带的斜长石以奥长石为主(An15.0-24.1);虎头崖矿床VI矿带的斜长石主要为钠长石和奥长石(An8.7-20.8);卡而却卡矿床B区的斜长石主要是中长石(An33.8-42.2);野马泉矿床的斜长石主要为奥长石和中长石(An26.2-48.4)。角闪石为典型的钙角闪石,其中,虎头崖矿床I矿带的角闪石属铁浅闪石;卡而却卡矿床B区的角闪石为镁角闪石和铁角闪石。各矿床(带)的黑云母普遍富Fe、Ti、F、Cl,属典型的铁黑云母。矿物学特征显示,各矿床(带)的黑云母结晶于相似的高氧逸度条件下,但在结晶温度和挥发份组成等方面存在差异。黑云母的结晶温度和氧逸度特征与各矿床类型之间未表现出明显的规律性特征。结合前人的研究成果可知,岩浆结晶的温度和氧逸度可能不是控制本区矽卡岩矿床成矿作用类型的主要因素。黑云母的挥发份组成与各成矿元素间表现出明显的规律性特征,其中,以Fe为主的虎头崖矿床I矿带和野马泉矿床的岩浆流体特征基本一致,表现出相对富Cl、贫H2O、F的特点;以Zn为主的虎头崖矿床VI矿带的岩浆流体相对富F贫H2O、Cl;以Cu为主的卡而却卡矿床B区的岩浆流体相对富Cl、H2O贫F,说明岩浆流体不同的挥发份组成可能与不同的矿床类型之间存在密切的联系。综合地质特征和矿物学特征可知,岩浆流体的挥发份组成可能是控制青海祁漫塔格地区矽卡岩矿床成矿作用类型多样性的重要因素之一。

Mineral characteristics of granitic rocks from skarn deposits, Qimantag area, Qinghai Province, East Kunlun, and its geological significance

The Qimantag area of Qinghai Province (hereafter referred to as QAQP), located within western part of East Kunlun orogenic belt, is one of the most important prospecting regions of China. In this study, we present new mineralogical data for granitic rocks associated with No.I section (Fe) of the Hutouya deposit (HD-I), Yemaquan Fe deposit (YD), No. B section (Cu) of the Kaerqueka deposit (KD-B) and No. VI section (Zn) of the Hutouya deposit (HD-VI) within the QAQP. Plagioclases of granitic rocks from the HD-I, HD-VI, YD and KD-B mainly belong to oligoclase (An_15.0-24.1), albite and oligoclase (An_8.7-20.8), oligoclase and andesine (An_26.2-48.4), and andesine (An_33.8-42.2), respectively. The hornblendes from the HD-I and KD-B mainly belong to ferro-edenite, and magnesiohornblende and ferrohornblende, respectively. The biotites are Fe-rich annite, and have high Ti, F and Cl concentrations. Mineral characteristics show that biotites in these rocks formed under similar oxygen fugacities, but have different temperatures of crystallization and magmatic fluid compositions. The crystallization temperatures and oxygen fugacities of these biotites do not show any associations with skarn types. According to the results of previous studies, we argue that the crystallization temperatures and oxygen fugacities of these biotites are not important factors in controlling skarn types in the QAQP. Biotite compositions show that the magmatic fluids associated with the KD-B (Cu) are characterized by high Cl, H₂O and low F fugacities; the magmatic fluids of the HD-VI (Zn) have high F, low H₂O and Cl fugacities; the magmatic fluids associated with the HD-I and YD (Fe) show characteristics of high Cl and low H₂O and F fugacities. This indicates that volatile compositions of magmatic fluids are associated with skarn types. Geological and mineralogical evidences indicate that volatile compositions of magmatic fluids play a key role in controlling the mineralization diversity within the QAQP.