S-Pb isotopes and tectono-geochemistry of the Lunong ore block, Yangla large Cu deposit, SW China: Implications for mineral exploration

Abstract

The Yangla Cu deposit is the largest Cu skarn deposit in the Jinshajiang Suture Zone, central Sanjiang region, SW China, with a total reserve of 150 Mt Cu @ 1.03%. The skarn orebodies are strictly controlled by the stratum, structure, and granitoid geometry, which are layered, lenticular, and vein-like within the contact or fracture zone between the granitoid and wall-rocks. Mineralization can be divided into three stages, pre-ore stage andradite and diopside, syn-ore stage sulfides-quartz-calcite, and supergene stage malachite, limonite, and azurite. In this study, the S-Pb isotopes and trace elements compositions of ore-related samples were determined. The S isotopes of pyrite, chalcopyrite, and pyrrhotite contained δ34S = -1.97 to 0.66‰, −2.48 to −1.76‰, and −1.93 to −1.67‰, respectively. This suggests that the S of hydrothermal minerals derived from granitic magma systems. The Pb isotopes of six sulfides consist of Pb isotope ratios of 206Pb/204Pb = 18.319 to 18.478, 207Pb/204Pb = 15.645 to 15.737, and 208Pb/204Pb = 38.516 to 38.799, respectively. This suggests that the granitic magma and host rocks contributed most of the Pb values, whereas the Beiwu Formation basalts have the least contribution to Cu mineralization. Hydrothermal fluid boiling is thought to be the most effective mechanism for the ore sulfide precipitation in the Yangla Cu deposit. Cluster analysis (CA) of the trace elements in ore-related samples indicates that trace elements may be divided into three groups: (i) Zn, Cd, Pb, Mo, and Ag; (ii) Ba, Tl, Cr, rare earth elements (REE), Hf, Nb, V, Sc, Li, Cs, Be, Ga, Ta, Rb, Th, Sr, and Zr; and (iii) Cu, In, Bi, Ge, Co, W, Sn, and U. Principal component (PC) analysis of trace elements suggests that trace elements can be divided into five principal components: PC1: Ga, Rb, Cs, Th, Be, Li, Ta, Ba, V, Sc, Hf, ∑REE2, and Tl; PC2: In, Cu, Sn, Ge, Bi, U, Co2, and W; PC3: Zn, Cd, Pb, Ag, Nb, Mo, and Tl2; PC4: Ni, Co, and (-Sn2); and PC5: Zr, Sr, ∑REE, Ta2, Cr, and Nb2. Combined with the geological setting and prospecting marks, structure, lithology, hydrothermal alteration, and tectono-geochemistry characteristics suggest that the key prospecting target areas D-1, D-2, and D-3 should be the significant mineral exploration targets. This constrains the future mineral exploration associated with Cu at the depths of the Lunong ore block, Yangla Cu deposit.