LA-ICP-MS in situ trace elements and FE-SEM analysis of pyrite from the Xinqiao Cu-Au-S deposit in Tongling, Anhui and its constraints on the ore genesis

Xinqiao deposit is one of most typical stratiform and stratoid copper-gold-sulfide deposits in Tongling ore concentration area of the Middle and Lower Reaches of Changjiang River metallogenic belt. Two types of pyrite were recognized through detailed field work and paragenetic studies. Textures and trace element composition of two types of pyrite has been studied by scanning electron microscope and laser ablation-inductively coupled plasma-mass spectrometry. FE-SEM analyses of two types of pyrite indicate that the Pyl is consisted of tiny cube pyrite with garin size of 100 ∼ 500nm, Pyll is consisted of medium-coarse octahedral and pentagonal crystal pyrite with garin size of 50 ∼ 100μm. LA-ICP-MS analyses of two types of pyrite indicate that the Pyl contains the highest values of As, Se, Te. Pyll pyrite enrich Cu, Pb, Zn, Au and Ag with variable content of ore-forming elements such as Bi,Co, Ni, V, Ti, Mg, Cr, Cd, Al, Mn. Textures, paragenesis and trace element geochemistry of pyrite indicate that Pyl was formed in the process of the Late Paleozoic submarine sedimentation, whereas Pyll pyrite may occur during the Mesozoic hydrothermal superimposition. Therefore, the formation of Xinqiao Cu-Au-S deposit may have recorded both the Late Paleozoic submarine or exhalation sedimentation and hydrothermal overprint in Mesozoic. Colloform pyrite without Cu and Au mineralization deposited during sedimentation, while most of economic metals, e. g., Cu, Pb, Zn, Au and Ag, were introduced through hydrothermal fluids during emplacement of the Yanshanian dioritic intrusions.