Abstract
Gold deposits in the Jiaodong Peninsula represent a primary gold resource in China and mostly exhibit similar ore-forming features related to sericite-quartz-pyrite alteration and other controls from (micro-)structural deformation. This study investigates the pyrite textures and trace elements in the Sizhuang gold deposit (>100 t Au) to document the key factors impacting on the genesis of the Jiaodong-type orogenic deposits. Three main types of pyrite are identified: (1) the first generation of pyrite (Py1) occurs as disseminated euhedral to subhedral grains in K-feldspar-albite-rutile-hematite and sericite alteration (stage 1), (2) Py2 as aggregates in quartz-sericite-pyrite altered rocks or quartz-pyrite veins (stage 2) can be subdivided into Py2a as irregular cores, Py2b as a zoned overgrowth on Py2a, and Py2c as overgrowth on early pyrite, and (3) Py3 as fine-grained crystals in siderite-polymetallic veins (stage 3). Primary gold at the Sizhuang deposit is coevally or slightly later deposited with Py2b, Py2c, and Py3. Laser ablation–inductively coupled plasma mass spectrometry (LA–ICP–MS) analyses show that the highest Co and Ni contents in Py1 and high but variable Co in Py2b favors the involvement of deep high-temperature magmatic waters at stage 1 and middle stage 2. The elevated As contents from Py2a to Py2c and depletion of trace elements (e.g., Co, Ni, As and Te) and high Au/Co, Cu/Ni, and As/Ni values in Py2a and Py3, combined with published H-O isotope data, imply a meteoric water ingress during stage 2–3. Thus, the fluid evolution at Sizhuang is a consequence of pulsed deep magmatic fluid release plus progressive meteoric fluid ingress. The rhythmic Co–As–Ni–Au bands of Py2b additionally suggest episodic changes in the composition of ore-forming fluids. Moreover, the sharp textural features (e.g., pyrite overgrowth on previously cataclastic crystals) of Py2 and As-Cu-rich and Co-poor bands in zoned Py2b probably also reflect rapid metal deposition and self-organization and subsequent mineral crystal growth due to the pressure release during phase separation in the Sizhuang deposit. Considering the significantly concentrated gold (>1300 t) in the regional Jiaojia fault zone and Au-bearing mineral formation related to phase separation (boiling) in the Sizhuang deposit, gold mineralization in the Sizhuang deposit was interpreted to be controlled by the pressure-driver owing to the seismic activities in the Jiaojia fault system.
Highlights
The Jiaodong Peninsula located in the eastern portion of the North China Craton
Most of the orogenic gold deposits in the Jiaodong Peninsula are hosted in NNE- or NE-striking detachment faults, such as the Sanshandao, Jiaojia, and Zhaoping faults, in the west Jiaobei terrane (Figure 1)
Mineral assemblages, textures, and relative relationships, three types of pyrite in the Sizhuang deposit have been recognized in this study
Summary
The Jiaodong Peninsula located in the eastern portion of the North China Craton Archean greenstone belts syn-metamorphic origin for orogenic gold deposits in Archean greenstone belts [3,13,14,15] For this reason, the term “Jiaodong-type orogenic deposit” has been proposed to distinguish. Pyrite often exhibits the cataclastic, zoned, and/or overgrowth textures associated with multiple micro-structural deformation events that, at least partly, control gold deposition from fluids in the Jiaodong gold deposits [18,51,52], providing an excellent record of the fluid kinetic environment during mineralization. We present a detailed investigation of pyrite textures and trace element chemistry of the Sizhuang pyrite to understand gold precipitation and fluid evolution of the Sizhuang deposit as well as the ore genesis of the Jiaodong-type orogenic deposits
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