Geology and geochemistry of telluride-bearing Au deposits in the Pingyi area, Western Shandong, China

• Published in: Mineralogy and petrology 2006-07, Vol.87 (3-4), p.209-240
• Main Authors: Hu, H.-B., Mao, J.-W., Niu, S.-Y., Li, Y.-F., Li, M.-W.
• Format: Article
• Language: English
• Subjects: Calcite; Cambrian; Carbonate rocks; Crystallization; Dolomite; Geochemistry; Geology; Gold; Jurassic; Limestone; Magma; Mineralization; Mineralogy; Ordovician; Pyrite; Sedimentary rocks; Sodium chloride; Sulfur
• ISSN: 0930-0708; 1438-1168
• DOI: 10.1007/s00710-006-0126-8

Telluride-bearing gold deposits of the Pingyi area, western Shandong, China, are located on the southeastern margin of the North China Craton. There are two main types of deposits: (i) mineralized cryptoexplosive breccia, e.g., Guilaizhuang; and (ii) stratified, finely-disseminated mineralization hosted in carbonate rocks, e.g., Lifanggou and Mofanggou deposits. In Guilaizhuang, the cryptoexplosive breccia is formed within rocks of the Tongshi complex and Ordovician dolomite. The mineralization is controlled by an E-W-trending listric fault. Stratified orebodies of the Lifanggou and Mofanggou deposits are placed along a NE-trending, secondary detachment zone. They are hosted within dolomitic limestone, micrite and dolomite of the Early-Middle Cambrian Changqing Group. The mineralization in the ore districts is considered to be related to the Early Jurassic Tongshi magmatic complex that formed in a continental arc setting on the margin of the North China Craton. The host rocks are porphyritic and consist predominantly of medium- to fine-grained diorite and pyroxene (hornblende)-bearing monzonite. SHRIMP U-Pb zircon dating of diorites give a 206 Pb/ 238 U weighted mean age of 175.7 +/- 3.8 Ma. This is interpreted as representing the crystallization age of the Tongshi magmatic complex. Considering the contact relationships between the magmatic and host sedimentary rocks, as well as the genetic link with the deposits, we conclude that this age is relevant also for the formation of mineralization in the Pingyi area. We hence consider that the deposits formed in the Jurassic. The principal gold minerals are native gold, electrum and calaverite. Wall-rock alteration comprises pyritization, fluoritization, silicification, carbonatization and chloritization. Fluid inclusion studies indicate that all the analyzed inclusions are of two-phase vapor-liquid NaCl-H 2 O type. Homogenization temperatures of the fluid inclusions vary from 103 degrees C to 250 degrees C, and the ice melting temperatures range from -2.5 degrees C to -13.5 degrees C, corresponding to a salinity range of 4.65 to 17.26 wt.% NaCl equiv. The [delta] 34 S values of pyrite associated with gold mineralization exhibit a narrow range of -0.71 to + 2.99[per thousand], implying that the sulfur was probably derived from the mantle and/or dioritic magma. The [delta] 13 C PDB values of the fluid inclusions in calcite range from -7.3 to 0.0[per thousand]. The [delta] 18 O SMOW values of vein quartz and calci