诸广三江口岩体黑云母地球化学特征及其地质意义

Geochemistry of Biotite from the Sanjiangkou Pluton in the Zhuguangshan Massif Terrane and Its Geological Significance

探究三九地区铀矿床中赋矿围岩中粗粒似斑状黑云母二长花岗岩中的黑云母矿物学特征,能较好地揭示该区产铀岩体的成岩成矿地质意义。本文对三江口岩体东段新鲜花岗岩中的黑云母进行了光学显微镜观察和电子探针分析。结果表明,新鲜黑云母晶形一般较完整,一般不含铀,少量黑云母边缘蚀变为绿泥石。具有富铁贫镁特征,属铁叶云母。通过计算得到黑云母结晶温度为583.6~631.6℃,lgfO2为-16.8^-18.0,岩体结晶压力为298.4~397.2 MPa,对应侵位深度为11.3~15.0 km。与前人研究的众多产铀岩体相比,三江口岩体具有相似的成岩特征,应有较大成矿潜力。

The Sanjiu area is located in eastern section of the Sanjiangkou pluton in central Zhuguangshan Massif. In recent years, the exploration of granite-related uranium deposits in the area has made great breakthroughs. Uranium mineralization is mainly hosted in the coarse-grained biotite adamellite, in which biotite bear information of petrogenesis and the process of uranium mineralization. The petrography and electron probe(EMPA)studies of the biotite from fresh granite in eastern Sanjiangkou pluton were carried out in this study. Fresh biotite is generally euhedral, which is free of uranium. Margin of some biotite have been altered to chlorite. Most biotites are iron-rich and magnesium-depleted, belonging to hydroxyl-siderophyllite. Biotite has crystallization temperature of 583.6-631.6 ℃, the lgfO2of-16.8——18.0. The crystallization pressure of pluton is 298.4-397.2 MPa, corresponding to the emplacement depth of 11.3-15.0 km. The Sanjiangkou pluton has similar origin with the other ore-bearing granites, suggesting a large potential of U mineralization.