蚀变矿物近红外光谱特征对地质找矿的指示意义——以甘肃岗岔金矿为例

甘肃岗岔金矿位于秦岭造山带之碌曲-成县逆冲推覆构造带的西段北侧,是典型的构造蚀变岩型金矿床,目前储量可达中型。在矿区地质填图的基础上,采用BJKF-1型近红外矿物分析仪对矿区7号勘探线ZK07-4钻孔、8号勘探线ZK08-6钻孔及27号勘探线的ZK27-1、ZK27-3、ZK27-4钻孔岩心进行蚀变特征研究,识别出的主要蚀变矿物为伊利石、云母类、地开石、高岭石等。蚀变矿物分布及含量变化特点表明,与矿化有关的蚀变主要是绢英岩化,其中已探明矿体多位于采用近红外分析技术圈出的绢英岩化带内。此外,伊利石反射光谱特征参数计算结果表明,伊利石结晶度和Al-OH特征吸收峰形态呈现有规律的变化,即含矿段和近矿段伊利石结晶度大(SWIR-IC值5.5~5.7),Al-OH吸收峰尖锐;远矿段和无矿段伊利石结晶度小(SWIR-IC值1.3~1.5),Al-OH吸收峰平缓,显示含矿段伊利石形成温度较高。上述结果表明,矿区内绢英岩化蚀变及伊利石结晶度、Al-OH峰形是有利找矿标志,对找矿具有实际指导意义。

The application of near-infrared spectroscopy to identify altered minerals and its implications for geologic prospecting: A case study of the Gangcha gold deposit in Gansu Province

Located on the northwestern side of Luqu-Chengxian thrust nappe zone in Qinling orogenic zone, the Gangcha gold deposit is a classical fractural alteration type gold deposit, in which the reserves of metal gold is up to medium scale. On the basis of geological mapping of the mining area, a BJKF-1 near-infrared mineral analyzer was used for drill hole ZK07-4 along No. 7 exploration line, drill hole ZK08-6 along No. 8 exploration line, and drill holes ZK27-1, ZK27-3, ZK27-4 along No. 27 exploration line to study the alteration characteristics. Some major alteration minerals were identified by the analyzer, which included illite, mica, dickite, kaolinite etc. According to the distribution and content changes of alteration minerals, phyllic alteration is related to mineralization, and the proven orebodies are mainly located in the phyllic alteration zone. Besides, a study of illite spectral reflectance parameters shows that illite crystallinity and Al-OH characteristic absorption peak patterns change regularly, that is to say that the ore part''s illite crystallinity is large (5.5~5.7), the absorption peak of Al-OH is sharp, the surrounding rock''s illite crystallinity is small (1.3~1.5), and the absorption peak of Al-OH is flat, suggesting that the ore-bearing part''s illite was formed at high temperature. These results suggest that phyllic alteration, illite crystallinity and Al-OH profile can be taken as the indicator of mineralization during mineral exploration.