EARLY VARISCAN SEDIMENTARY BASIN SPREADING AND HYDROTHERMAL MINERALIZATION IN NORTHERN GUANGDONG

The half graben-like rifted basin in northern Guangdong was controlled by a trifurcate spreading basin system within the South China plate during Late Palaeozoic time.The sedimentary evolution has undergone several stages of basement uplifting,extensional faulting,subsidence (delta infilling),submergence and closure,of which the subsidence and early stable stages are believed to be favourable for hydrothermal mineralization.The hydrothermal(exhalative)ore deposits are generally characterized by the "sandwich" ore sequence:footwall alteration (vein ores)→concordant massive sulfide ore bodies→roof alteration and/or exhalative cover,and explosing and boiling features at the bottom of the sequence.The hydrothermal sedimentary(exhalative)rocks have lower negative δ¹³C and δ¹⁸O values than those of the normal marine silicolites,and REE patterns with strong Euanomalies.
Four mineralization-related thermal events have been distinguished in the early Variscan cycles.They once occurred in the Middle Devonion,Upper Devonian,Middle and Upper Carboniferous and Lower Permian.The authors conclude that most of the massive sulfide deposits in the study area were generated in the early stage of basin spreading, whereas the other (e.g.Au,Ag and Cu)ore deposits were formed during the Indosinian-the closure stage of the basin.