滇西北中甸铜厂沟燕山期斑岩型Mo-Cu矿床热液蚀变分带结构及发育机制

The Zhongdian area is located in the southern section of Yidun island arc belt and is an important copper-molybdenum polymetallic mineral resources base in Sanjiang area of southwestern China. Since the Late Triassic, the subduction of oceanic crust had led to the formation of porphyry Cu polymetallic deposits. In Late Cretaceous, due to the shortening and the thickening of the crust, partial melting of lower crust occured during the lithospheric mantle subsidence. This caused granitic magma emplacing in an extended environment after collision, accompanied by the formation of Mo(Cu) polymetallic mineralization. The Tongchanggou porphyry Mo-Cu deposit is located at the southern tip of Zhongdian area and it is a typical representative of the Late Cretaceous mineralization in the region. Based on the previous studies, the application will find out the structure characteristics of the mineralization-alteration zone by finely dissecting the Mo-Cu deposit alteration and vein system at Tongchanggou. Geological fluids in different metallogenic stages are going to be studied to ascertain the physical and chemical conditions and composition differences of the ore-forming fluids. Through the effective identification of geologic records of magmatic-hydrothermal process and micro-analysis of individual inclusions, the initial fluid properties of the magmatic exsolution and the process will be explored, and the evolutionary process of magma-fluid-mineralization will be remodeled to futher reveal the mechanism of deposit formation and to construct a porphyry Mo-Cu deposit metallogenic model that meets the post-collisional extension environment of the Late Cretaceous in Zhongdian, which would provide a scientific basis for geological prospecting in this area.

滇西北中甸地区位于义敦岛弧带南段，是西南三江重要的铜钼多金属矿产资源基地。该区自印支期以来，伴随洋壳的俯冲消减，形成了斑岩型Cu多金属矿床；燕山期，受地壳缩短和加厚的影响，在岩石圈地幔拆沉过程中下地壳发生部分熔融作用，导致碰撞后伸展环境的花岗质岩浆侵位，并伴有Mo（Cu）多金属成矿作用的形成。铜厂沟斑岩型Mo-Cu矿床位于中甸地区南端，是区内燕山期成矿作用的典型代表。本申请在前期研究工作基础上，通过精细解剖铜厂沟Mo-Cu矿床蚀变与脉体系统，查明矿化-蚀变分带结构特征。开展不同成矿阶段地质流体研究，查明成矿流体的物理化学条件和组分差异。通过岩浆-热液过程地质记录的有效识别与单个包裹体的微区分析，探讨岩浆出溶的初始流体性质及出溶过程，重塑岩浆-流体-成矿作用的演化过程，深入揭示矿床形成机理，构建符合云南中甸燕山期碰撞后伸展环境的斑岩型Mo-Cu矿床成矿模式，为该区地质找矿提供科学依据。

铜厂沟钼铜矿床位于云南中甸地区斑岩成矿带的南端，形成于燕山晚期陆-陆碰撞至造山后伸展构造的转换阶段，是区内晚白垩世钼铜多金属成矿作用的典型代表之一。本项目通过对铜厂沟钼铜矿床地质特征、蚀变分带特征和脉体穿切关系的详细解剖，系统厘定了矿床蚀变类型及空间分布规律，查明了蚀变和脉体系统与矿化的关系。研究表明，铜厂沟钼铜矿床蚀变类型主要有钾硅酸盐化（KSi）、石英-绢云母化（SiSe）、青磐岩化（CHEp），以及矽卡岩化（带）。根据脉体中矿物组合及其形态、蚀变类型等因素分为A脉、B脉和D脉三类，共16种不同的脉体类型。成矿阶段由早到晚分为钾长石-石英阶段（Ⅰ）和石英-硫化物阶段（Ⅱ）及石英-石膏阶段（Ⅲ），其中Ⅱ阶段是主要成矿阶段，可细分为石英-黄铁矿（Ⅱ-1）、石英-黄铁矿-辉钼矿（Ⅱ-2）、石英-辉钼矿（Ⅱ-3）等3个亚阶段。流体包裹体测温和氢-氧同位素研究显示，成矿流体早期为H2O-NaCl-CO2体系，演化晚期为H2O-NaCl体系，总体从高温中等盐度岩浆流体向中温中（低）盐度富CO2流体演化，直至大气降水大量混入而形成中低温、低盐度的混合流体，成矿过程中沸腾作用、降压降温、CO2逸失是该矿床的重要形成原因。铜厂沟花岗闪长斑岩的岩体侵位的深度约为4.3 km～9.9 km，具中深成侵位的特点，斑岩体形成于较高的fO2条件。通过对中甸铜钼多金属矿集区晚三叠世和晚白垩世代表性体斑岩的锆石氧逸度差异性成矿进行研究表明，俯冲或碰撞环境的斑岩型铜矿，高氧逸度是成矿的必要非充分条件；碰撞型斑岩矿床钼、钨主要来自古老地壳，对氧逸度的要求相对较低，偏氧化环境有利钼矿形成，偏还原环境有利于钨矿形成。铜厂沟斑岩型钼铜矿床的形成与区内燕山晚期伸展作用相伴的大规模构造-岩浆事件密切相关，有利的构造环境、强烈的岩浆作用、多源的物源条件是铜厂沟大型斑岩型钼铜矿床最终得以形成。