新疆阿尔泰巴斯铁列克钨多金属矿区花岗岩黑云母特征及成岩成矿意义

黑云母是花岗质岩石中常见的造岩矿物，其成分可以有效指示花岗岩形成的物理化学条件和岩石成因。巴斯铁列克矿床是近年来在新疆阿尔泰造山带南缘发现的首例二叠纪矽卡岩型钨多金属矿床。矿区出露多种类型二叠纪含钨花岗岩。为理清花岗质岩体之间、岩体与钨多金属矿化之间的关系，文章采用电子探针测定了黑云母花岗岩、二长花岗岩、二云母花岗岩和钾长花岗岩中的黑云母成分。结果表明，所有黑云母具有富铁、高铝、贫镁特征，含铁指数(Fe²⁺/(Mg+Fe²⁺))为0.66~0.80，二云母花岗岩属铁质黑云母而黑云母花岗岩、二长花岗岩和钾长花岗岩属铁叶黑云母。所有岩石是具有A型特征的I型花岗岩。不同类型岩石中黑云母的成分差异与岩浆来源、分异演化程度有关。二云母花岗岩中黑云母的w(MgO)与结晶温度最高，与黑云母平衡流体的log(fHF/fHCl)值（-1.13~-1.25）最低，log(fH₂O/fHF)值（4.64~4.96）最高，母岩浆相对富Cl；黑云母花岗岩中log(fHF/fHCl)值最高，log(fH₂O/fHF)最低，与二长花岗岩是同一岩浆房不同演化阶段的产物，与二云母花岗岩和钾长花岗岩属不同的岩浆体系，母岩浆相对富F元素。黑云母花岗岩与W矿化关系更密切。

Geochemical characteristics of biotite from granites around Bastielieke W-polymetallic deposit in Altay, Xinjiang and its implication

Biotite is an important rock-forming mineral in granitoids, and is also a good proxy for chemical and physical conditions associated with crystallization from the magma, and petrogenesis. The Bastielieke deposit is a medium-size W-polymetallic skarn deposit in Xinjiang Altay. Its skarn ores are mainly hosted at/near the contact between the Kangbutiebao and Permian granites. Permian granitoids are composed of several pulses of magmas. However, the interrelationship of these different granites, specific intrusive phases related to mineralization is little known. Electron microprobe analyses on primary magmatic biotites from biotite granite, monzogranite, twomica granite, and K-feldspar granite are performed to investigate magmatic processes, associated hydrothermal fluids, and contributions to mineralization. The results show that the magmatic biotite grains have X_Fe=Fe²⁺/(Mg+ Fe²⁺)] values ranging from 0.66 to 0.80, and they belong to ferribiotite in two-mica granite and siderophyllite in other three intrusions. These granites are similar to the geochemical behavior of the fractionated I-and A-type granitoids. The magma source and fractional crystallization degree may be responsible for the differentiation of biotite compositions. Compared with other three intrusions, two-mica granite appears to have higher MgO contents and magmatic temperatures. The halogen fugacity of magmatic fluid calculated from biotite composition has the lowest log (fHF/fHCl) ratios (-1.13~-1.25) and highest log (fH₂O/fHF) ratios (4.64~4.96), showing high Cl in fluids. The biotite granite shows the highest log (fHF/fHCl) ratios (-0.59~-0.81) and lowest log (fH₂O/fHF) ratios (4.18~4.52), and displays a differentiation trend from monzogranite, indicating their same magma origin. Biotite granite and monzogranite have different magma source and fractional crystallization degree from two-mica granite and K-feldspar granite. Biotite granite is favorable for W mineralization due to the highest evolution degree and high F in fluids.