西藏玉龙斑岩铜矿床绢云母族蚀变矿物短波红外光谱特征及对勘查的指示意义

Characteristics of short wave infrared spectroscopy of sericite group minerals and their implications for exploration in the Yulong porphyry copper deposit,Tibet

玉龙斑岩铜矿晚期绢云母化、黏土化蚀变强烈叠加在早期的钾硅酸盐化带内,模糊了蚀变分带特征及其与铜矿化之间的相关性。利用短波红外光谱(SWIR)可快速识别斑岩铜矿床内含羟基蚀变矿物,根据该类矿物的空间分布特征与矿化的对应关系,指导找矿勘查工作。本文对玉龙铜矿床靠近斑岩体中心的三个钻孔进行了详细的蚀变-矿化编录和SWIR分析,在识别出高岭石、蒙脱石、绢云母族矿物(绢云母、多硅白云母)、绿泥石等蚀变矿物的基础上,重点剖析了绢云母族矿物空间分布规律及其与铜矿化之间的相关性。研究表明:深部富铜矿体(Cu>0.6%)紧贴斑岩体侵位中心产出,与绢云母族矿物在空间上紧密伴生,且靠近岩体中心多硅白云母相对发育,绢云母族矿物Al-OH吸收峰值较大(Pos2200>2207 nm)、结晶度较高(IC>2.0);靠近岩体中心外围矿体时,绢云母族矿物Pos2200值相对较小(2206~2207 nm)、IC值相对较低(1.0~2.0)。因此,绢云母族矿物高Pos2200值(>2207 nm)和高IC值(>2.0)以及多硅白云母的出现可作为紧贴斑岩体外围矿体产出的底界线,而绢云母族矿物相对低的Pos2200值(2206~2207 nm)和较低的IC值(1.0~2.0)可作为深部富铜矿体出现的标志。

The late phyllic and clay alteration of Yulong porphyry copper deposit is strongly superimposed within the early potassic alteration,blurring alteration zonation and its correlation with copper mineralization.Using short-wave infrared spectroscopy(SWIR)can identify OH-bearing alteration minerals in porphyry copper deposits and identify alteration mineralization centers based on their spatial distribution.In this paper,we conduct detailed alteration-mineralization catalogs and SWIR analysis of three drill holes near the porphyry center of the Yulong copper deposit.Based on the identification of kaolinite,montmorillonite,sericite group minerals(sericite and phengite),chlorite and other alteration minerals,the spatial distribution patterns of sericite group minerals and their correlations with copper mineralization are emphatically analyzed.This study reveals that the deep Cu-rich ore bodies(>0.6 wt%)are immediately adjacent to the intrusion center of the porphyry body and are spatially associated with sericite.The phengite is relatively developed in the center of the rock body,and the absorption peak wavelength of the Al-OH of sericite group minerals is larger(Pos2200>2207 nm)and the crystallinity is high(IC>2.0).The Pos2200 values and IC values of the sericite group minerals are relatively smaller(2206~2207 nm)and lower(1.0~2.0)when close to the peripheral ore body of rock center.Therefore,high Pos2200 values(>2207 nm),high IC values(>2.0)of sericite group minerals and occurrence of phengite can be used as the bottom boundary of ore bodies,while the relatively lower Pos2200 values(2206~2207 nm)and lower IC values(1.0~2.0)of sericite group minerals can be used as an indication of the occurrence of deep copper-rich ore bodies.