Tectono-Magmatic Setting of the Divar Deposit, Eastern Iran: Evidences for VMS Mineralzation

The Divar VMS deposit is located in the Nehbandan ophiolite complex (NOC). It is 10 hosted in the Sistan suture zone (SSZ) marking the boundary between the Lut and Afghan 11 continental blocks. This area is composed mainly of various ophiolitic rock units representing a 12 tectono-sedimentary mélange, which are commonly interpreted as being the remnants of Sistan 13 oceanic lithosphere. The major host rocks cropping out in the Divar deposit are mantle peridotites 14 include clinopyroxene(cpx-) rich harzburgites and depleted harzburgites with gabbronorite, 15 cumulate gabbro, basalt and pelagic sediments. They are interpreted as being related to the rifting 16 and subsequent Late Triassic continental break-up of the southern Neothethys. In this study 17 petrographic observations mineral chemistry with whole rock chemistry, and rare earth element 18 (REE) modeling were carried out on the different rocks associated with Divar deposit. The 19 presented data led to the following conclusions: (1) The depleted harzburgites proved to be related 20 to the residual mantle after 18–22% removal of melts. This is comparable with abyssal peridotites; 21 (2) The cpx-rich harzburgites represent the residual mantle after the removal of 11–13% mid-ocean 22 ridge basalt-type (MORB). Subsequently, the residual mantle was enriched in light REE (LREE) by 23 subduction-derived fluids; (3) The gabbronorite and cumulate gabbro represents a portion of 24 oceanic crust generated in a mid-ocean ridge setting; (4) The basalts belong to the N-MORB-type 25 with no considerable crustal contamination. From the top to bottom, the Divar deposit is 26 characterized a gossan zone, a thick massive ore zone, and a poorly developed stockwork zone. In 27 Divar deposit, host rocks are indicated by serpentinized peridotites and severely altered mafic 28 rocks that include disseminated and stockwork ore under massive lenses. These rocks showed a 29 mineral assemblage of carbonate + quartz-jasper + chlorite + albite + epidote that demonstrate 30 greenschist facies ocean floor metamorphism. Moreover, in the footwall rocks, sericitization and 31 hematitization are also observed. Primary mineralization includes bedded ore, sulphide breccias, 32 stockworks and chimney fragments. Ore mineral abundances decrease from pyrite, magnetite, to 33 chalcopyrite, and sphalerite. Highlightly, there are two distinct mineralization phases' namely 34 massive sulphide (stage-1) and massive magnetite (stage-2). The spatial relationships with the host 35 rocks and textural evidence (e.g., magnetite replacing sulphides) indicate that sulphide minerals 36 and magnetite were generated in different stages. The transition from sulphide to magnetite 37 mineralization is interpreted as being related to the variation of H2S content in the ore fluids. The 38 massive sulphide ore (stage 1) might have formed by primary hydrothermal fluids enriched in H2S 39 and Fe. The second stage (massive magnetite) seem to be related to the later hydrothermal fluids 40 enriched in Fe but poor in H2S, replacing the pre-existing sulphide minerals. The lithological 41 features (stockwork/massive ore and gossan), mineral paragenesis and alteration patterns of the 42 Divar deposit are all consistent with a Cyprus-type VMS system mineralization. However, 43 magnetite formation after the early sulphide mineralization is quite different with typical 44 Cyprus-type VMS deposits where magnetite commonly occurs in lower sections. Consequently, 45 although the general features of Divar deposit is analogous to those of Cyprus-type deposits, but 46 strong magnetite mineralization especially in late stages may indicate that this deposit could be 47 considered as an exceptional Cyprus-type VMS deposit. 48 Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 31 October 2017 doi:10.20944/preprints201710.0193.v1 © 2017 by the author(s). Distributed under a Creative Commons CC BY license.