Mineral chemistry of chlorite in different geologic environments and its implications for porphyry Cu ± Au ± Mo deposits

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 (chlorite PCDs ) and chlorite formed in other geological environments (chlorite Barren ). Here, based on occurrences, mineral assemblages, and compositions of the chlorites from thirty PCDs and barren areas (including geothermal systems , chlorite GSs ; low-grade metamorphic rocks , chlorite LGMRs ; sedimentary rocks, chlorite SRs ), we used principal component analysis (PCA) and random forest (RF) methods to find discrimination approaches. Results show that chlorite PCDs and chlorite Barren differ in the Fe, Mg, Al, Ti, and possibly Mn, K, and Ca elements. Based on these differences, wt.% ratios of (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), and FeO/100TiO 2 and diagrams of Fe/(Fe + Mg) (a.p.f.u. ratio) vs TiO 2 /(Na 2 O + K 2 O + CaO) (wt.% ratio), Fe/(Fe + Mg) (a.p.f.u. ratio) vs MgO/(100*Na 2 O*CaO) (wt.% ratio), and Fe/(Fe + Mg) (a.p.f.u. ratio) vs SiO 2 /Al 2 O 3 (wt.% ratio) are proposed to distinguish chlorite PCDs from chlorite Barren . These discrimination approaches have better results in distinguishing chlorite PCDs from chlorite LGMRs and chlorite SRs but are less effective for chlorite GSs . 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 chlorite PCDs and chlorite Barren . Although further researches remain to be done, this study provides potential approaches for identifying chlorite PCDs based on major elements.