School of Earth & Environmental Science
Walsh, Jessica MJ, Mineral Deposits and Tectonic Evolution of the Qinling Orogenic Belt, Central China, BSc Hons, School of Earth & Environmental Science, University of Wollongong, 2015.
Synthesizing the tectonic evolution of collisional orogens provides an important framework with which to place spatial and temporal constraints on the formation of various ore deposits in complexly deformed rocks. The Qinling Orogenic Belt (QOB), central China represents a composite orogen that has experienced four main episodes of accretion, subduction and subsequent collision between discrete continental blocks. Multiple tectonic events, from rifting to arc collisions to continental collisions since the Proterozoic have formed an orogen with
an abundant and diverse suite of mineral deposits. Although there are several metallogenic epochs throughout the geological evolution of the QOB and the adjacent areas including the North China Block and South China Block, the most pervasive, voluminous and abundant is the large-scale granite-related (Mo, Cu) event that occurred during final continental collision in the Mesozoic. This event saw the widespread emplacement of porphyry Mo-(Cu ± Au) deposits which were directly influenced by a post-collisional extensional regime, and subsequent influx of large-scale granitoid intrusives. Two mineralised aplite samples collected from the Nantai porphyry-skarn
Mo-(Cu) deposit were dated via SHRIMP zircon U-Pb methods at ANU and revealed an age of
151 – 148 Ma. The granites display geochemical patterns consistent with A-type granites but transitional towards S-type. Folded and faulted Devonian sedimentary sequences are host to high- grade Carlin-type and orogenic gold deposits, which are spatially and temporally associated with the Mesozoic granitoids (158 – 100 Ma). The Longtougou and Liujiaxia orogenic Au deposits are representative of this suite of gold deposits and mineralisation is thought to be coincident with the main post-Devonian deformation event responsible for folding and faulting of the Devonian units, possibly related to continental collision and voluminous magmatism in the Triassic. Other unusual deposit types include REE-hosting carbonatites within the South Qinling Belt. These are thought
to be Permo-Triassic in age and related to the voluminous alkali basaltic dyke swarms that intrude much of the Qinling Orogen. Petrographic and geochemical analysis of these rocks suggests they may have formed via the interaction of highly fractionated, alkalic silica-poor magmas which may have interacted with the abundant limestone country rocks to produce the carbonatite magmas and associated REE mineralisation. The formation and deformation of the QOB has been intensely debated from the onset of the earliest evolutionary histories and tectonic frameworks. This investigation provides the first multi-deposit approach to supplement the knowledge and broader literature on the development of the region.