Abstract
The Narusongduo Pb-Zn deposit is located at the northern boundary of the Luobadui-Milashan fault zone (LMF) in central Tibet and is spatially associated with the Linzizong volcanic succession (LVS). Our study indicates that the regional structural setting was formed by two-stage tectonic events. The first stage, spanning from the late Mesozoic to early Paleocene, is characterized by significant N-S crustal shortening associated with the Cordilleran-type orogeny along the Gangdese arc. The region's Paleozoic-Mesozoic metasedimentary rocks were penetratively strained. Locally deformation was largely partitioned along the LMF. During the second stage (ca. 66–55 Ma), the area was affected by extensive multi-stage Linzizong volcanism, including caldera formation, as well as a coaxial N-S propagative deformation with a distinctive lower shortening rate. We recognized two types of mineralization, both were formed during the second stage. The first type of mineralization (orebody III) is governed by fractures within the extensively deformed Paleozoic carbonate rocks at the LMF's footwall. The overlying LVS, however, includes discrete but numerous mineralized sections. The terminal splays of the ore shoots typify the products of hydraulic fracturing. We propose that the propagative compressive deformation drained fluid reservoirs at depth to higher levels via the “Fault valve” effect. Episodic fluid influxes and mineral deposition formed the time-integrated mineralization. The second type of mineralization (orebody I) is hosted in the LVS in a number of breccia pipes and dykes that were controlled by the structural weaknesses generated by the intersection of the radial and ring fractures. Mineralization occurs as veinlets in the matrix and clasts inside the breccias, which are characterized by multi-stage brittle cracking, fluid injection and mineral precipitation. It is interpreted that the multi-stage magmatism (ca. 66–55 Ma) triggered repeated hydrothermal activities and incremental mineralization within the ore-bearing breccia bodies.
Highlights
Hydrothermal mineralization usually occurs in volcanic environ ments as a result of a variety of processes such as eruption, brecciation, and extensive fluid circulation. (e.g., Hedenquist and Matsuhisa, 1987; White and Hedenquist, 1990; Sidorov et al, 2015; Nadeau et al, 2016; Guo et al, 2020a)
Structural controls on the formation of ore deposits hosted in fault zones, which are affected by intensive volcanism, are less clear and may vary significantly
It has been proposed that the Gangdese retro-arc thrust-fold belt accommo dates over 200 km of N-S shortening in the Lhasa terrane (Kapp et al, 2007a, 2019)
Summary
Hydrothermal mineralization usually occurs in volcanic environ ments as a result of a variety of processes such as eruption, brecciation, and extensive fluid circulation. (e.g., Hedenquist and Matsuhisa, 1987; White and Hedenquist, 1990; Sidorov et al, 2015; Nadeau et al, 2016; Guo et al, 2020a). Large-scale centric volcanism overprinting a pre-existing regional structural discontinuity would (1) induce repetitive magmatism and fluid ingres sion focusing on the regional structural weakness and (2) form relatively intact volcanic loads that may blanket later-stage fluid influx (Tram parulo et al, 2018 and references therein) This complexity highlights the necessity of investigation on the structural settings of this type of ore deposits. We conducted (1) geological mapping and structural analyses to reveal the structural frame of the Narusongduo region; (2) field and micro scopic observations to investigate the characteristics of the fracture and void systems and their controls on the mineralization, and present (3) a discussion on the possible mineralization model with the newly obtained structural and zircon U-Pb chronological data They provide new insight into the structural controls on Pb-Zn mineralization in the Gangdese retro-arc zone. This contribution sheds new light on our under standing of the generation of ore deposits in a compressional deformed site affected by intensive volcanism
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
