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Mineral chemistry of chlorite in different geologic environments and its implications for porphyry Cu ± Au ± Mo deposits
Ore Geology Reviews ( IF 3.2 ) Pub Date : 2022-09-21 , DOI: 10.1016/j.oregeorev.2022.105112
Changhao Li , Ping Shen , Yong Zhao , Pei Li , Lejun Zhang , Hongdi Pan

In the porphyry Cu ± Au ± Mo deposits (PCDs), chlorite and its mineral assemblages are indicators for exploration. However, chlorite found in PCDs may have different origins because it is a common mineral in different geological environments. Therefore, it is necessary to identify the differences in the composition of PCDs-related chlorites (chloritePCDs) and chlorite formed in other geological environments (chloriteBarren). Here, based on occurrences, mineral assemblages, and compositions of the chlorites from thirty PCDs and barren areas (including geothermal systems, chloriteGSs; low-grade metamorphic rocks, chloriteLGMRs; sedimentary rocks, chloriteSRs), we used principal component analysis (PCA) and random forest (RF) methods to find discrimination approaches. Results show that chloritePCDs and chloriteBarren differ in the Fe, Mg, Al, Ti, and possibly Mn, K, and Ca elements. Based on these differences, wt.% ratios of (MgO + 100*TiO2)/(FeO + 100*CaO), TiO2/(CaO + K2O + Na2O), Al2O3/(100*K2O*CaO), MgO/(100*CaO*Na2O), SiO2/100(CaO + K2O), and FeO/100TiO2 and diagrams of Fe/(Fe + Mg) (a.p.f.u. ratio) vs TiO2/(Na2O + K2O + CaO) (wt.% ratio), Fe/(Fe + Mg) (a.p.f.u. ratio) vs MgO/(100*Na2O*CaO) (wt.% ratio), and Fe/(Fe + Mg) (a.p.f.u. ratio) vs SiO2/Al2O3 (wt.% ratio) are proposed to distinguish chloritePCDs from chloriteBarren. These discrimination approaches have better results in distinguishing chloritePCDs from chloriteLGMRs and chloriteSRs but are less effective for chloriteGSs. By comparing the physicochemical conditions, the highly oxidized conditions and high temperature of the ore-related intrusions and fluid properties result in the compositional differences between chloritePCDs and chloriteBarren. Although further researches remain to be done, this study provides potential approaches for identifying chloritePCDs based on major elements.



中文翻译:

不同地质环境中绿泥石的矿物化学及其对斑岩型铜±金±钼矿床的影响

在斑岩型 Cu ± Au ± Mo 矿床 (PCDs) 中,绿泥石及其矿物组合是勘探指标。然而,在 PCD 中发现的绿泥石可能有不同的来源,因为它是不同地质环境中的常见矿物。因此,有必要识别与 PCDs 相关的绿泥石(chlorite PCDs)与其他地质环境中形成的绿泥石(绿泥石贫瘠)的成分差异。在这里,基于来自 30 个 PCD 和贫瘠地区(包括地热系统,绿泥石GS;低品位变质岩,绿泥石LGMR;沉积岩,绿泥石SR )的产状、矿物组合和组成),我们使用主成分分析 (PCA) 和随机森林 (RF) 方法来寻找辨别方法。结果表明,绿泥石PCD和绿泥石Barren在 Fe、Mg、Al、Ti 以及可能的 Mn、K 和 Ca 元素方面存在差异。基于这些差异,(MgO + 100*TiO 2 )/(FeO + 100*CaO)、TiO 2 /(CaO + K 2 O + Na 2 O)、Al 2 O 3 /(100* K 2 O*CaO)、MgO/(100*CaO*Na 2 O)、SiO 2 /100(CaO + K 2 O)、FeO/100TiO 2和Fe/(Fe + Mg)(apfu比)图与 TiO 2 /(Na 2O + K 2 O + CaO) (wt.% ratio), Fe/(Fe + Mg) (apfu ratio) vs MgO/(100*Na 2 O*CaO) (wt.% ratio), 和 Fe/(Fe + Mg) (apfu ratio) vs SiO 2 /Al 2 O 3 (wt.% ratio) 被提议用来区分绿泥石PCD和绿泥石Barren。这些鉴别方法在区分亚氯酸盐PCD与亚氯酸盐LGMR和亚氯酸盐SR方面具有更好的效果,但对亚氯酸盐GS的效果较差. 通过物化条件比较,成矿侵入体的高度氧化条件和高温以及流体性质导致绿泥石PCDs和绿泥石贫瘠的成分存在差异。尽管仍有待进一步研究,但本研究提供了基于主要元素识别亚氯酸盐PCD的潜在方法。

更新日期:2022-09-24
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