Alteration mineral identification and metallogenic prediction of porphyry deposits based on geochemical data
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摘要:
传统的勘查地球化学工作侧重于成矿元素异常的提取、解释和评价, 忽略了与成矿作用相关的其他主、微量元素可能提供的找矿信息, 无法有针对性地从地球化学数据中开展蚀变矿物提取并指导找矿。本研究以矿物学的角度从地球化学数据中提取蚀变矿物并对研究区进行了成矿预测, 介绍了以地球化学数据为基础、以矿物化学式中不同元素间化学计量数比值为理论基础的蚀变矿物提取新方法——一般元素比分析法。基于北山造山带高石山地区1∶2.5万岩屑地球化学测量获得的地球化学数据研究表明, 从SiO2、Al2O3、Na2O、K2O等数据中可有效识别出与斑岩型矿床密切相关的绢云母、钾长石等蚀变矿物, 其中绢云母沿岩体边缘分布, 钾长石多集中分布于岩体的中心部位。综合提取出的蚀变矿物和岩浆岩、构造、传统化探异常等控矿因素和找矿信息, 进一步对研究区开展了证据权重法成矿预测, 共圈定靶区5处。本研究提取的蚀变信息在野外调查工作中得到了验证, 表明一般元素比分析法提取蚀变矿物是可行的, 可在传统成矿预测方法的基础上进一步提供关键找矿信息。
Abstract:Objective Traditional exploration and geochemical studies have primarily focused on the extraction, interpretation and evaluation of metallogenic element anomalies. This approach, however, overlooks valuable ore prospecting information, which may be provided by other major and trace elements. Consequently, altered minerals cannot be effectively extracted, and geochemical data is under utilized for ore prospecting. Therefore, the author extracts alteration minerals from a mineralogical perspective and make metallogenic prediction.
Methods This paper introduces a new method for extracting alteration minerals based on geochemical data and the stoichiometric ratios of different elements in the mineral chemical formula, referred to as the general element ratio analysis.
Results Based on geochemical data obtained from 1∶ 25 000 debris geochemical survey in the Gaoshishan area of the Beishan orogenic belt, results show that sericite, K-feldspar and other alteration minerals are closely related to porphyry deposits, which can be effectively identified from SiO2, Al2O3, Na2O, K2O and other data. The mapping results reveal that sericite is mostly distributed along the intrusion's margins, while K-feldspar is mainly concentrated in the center of theintrusion. Then, based on the ore-controlling factors and ore-prospecting information, such as alteration minerals, magmatic rocks, structures, and traditional geochemical anomalies. This study further conducts metallogenic prediction for the Gaoshishan area using the weight-of-evidence method, delineating five target areas.
Conclusion The alteration information extracted in this study has been validated through field investigations confirming that the proposed method is feasible and can provide critical prospecting insights beyond those offered by traditional metallogenic prediction methods.
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图 2 Pearce元素比分析法原理图解(a1)和一般元素比分析法原理图解(b1) (据文献[19]修改)
dA/dC, dB/dC为岩石中迁移元素a, b, c摩尔数的变化趋势;m为守恒元素
Figure 2. Schematic diagrams of Pearce element ratio analysis(a1) and general element ratio analysis(b1)
图 6 高石山地区1∶2.5万岩屑地球化学测量Cu-Mo-Au等6种元素异常与蚀变矿物空间关系(地质底图图例同图 3)
Figure 6. Spatial relationship between six element anomalies such as Cu-Mo-Au and altered minerals from 1∶25 000 debris geochemical survey in the Gaoshishan area
图 7 高石山地区斑岩型铜钼金多金属矿证据权重法成矿预测图(地质底图图例同图 3)
Figure 7. Metallogenic prediction map of porphyry Cu-Mo-Au polymetallic deposit in the Gaoshishan area by evidence weight method
表 1 常见蚀变矿物化学式
Table 1. Chemical formula of common altered minerals
矿物 化学式 高岭土 Al4(Si4O10)(OH)8 绢云母 KAl3Si3O10(OH)2 碳酸盐类 Ca(Fe, Mg)(CO3)2 钠长石 NaAlSi3O8 钾长石 KAlSi3O8 石膏 CaSO4 表 2 高石山地区斑岩型铜钼金多金属矿成矿预测各证据因子及其权重值
Table 2. Evidence factors and weight values for metallogenic prediction of porphyry Cu-Mo-Au polymetallic deposit in the Gaoshishan area
证据因子种类 证据因子名称 正权重值W+ 负权重值W- C 地质变量 绢云母缓冲区500 m 1.06 -0.68 1.74 钾长石缓冲区500 m 0.00 -0.08 0.08 酸性-中酸性侵入岩缓冲区300 m 0.28 -0.67 0.95 断裂构造缓冲区300 m 0.11 -0.20 0.31 地球化学变量 Cu 1.97 -0.83 2.80 Mo 1.95 -0.45 2.40 Au 2.26 -1.52 3.78 Ag 2.15 -0.84 2.99 Pb 0.89 -0.14 1.03 Zn 1.57 -0.42 1.99 注:C=W+-W-,表示证据层与矿床(点)证据层的相关程度 -
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