Identifying and Comparing the Exploration Criteria at Sari Gunay Gold, Dalli Copper-Gold and Zarshuran Gold Deposits in Zagros Orogen

Abstract

There are important deposits such as Sari Gunay epithermal gold, Dalli porphyry copper-gold, and Zarshuran Carlin deposits with a few common exploration features in the Zagros metallogenic province of Iran. This study used geological maps, remote sensing, geochemical, geophysical, mineralogical, petrographic, fluid inclusion and age dating information to characterize and identify exploration criteria of these deposits. Mineralization at Sari Gunay gold deposit is epithermal, which was formed in association with an alkaline magma and brecciated, altered dacite porphyry about 11 Ma. Mineralization at Zatshuran is Cralin with black shale and carbonate sedimentary hosts, formed indirectly in association with a deep alkaline magma about 14 Ma. Mineralization at Dalli deposit is copper-gold porphyry with diorite host, formed in association with a chalk alkaline magma about 21 Ma. Despite different host rocks, mineralization at Zarhuran and Sari Gunay gold deposits reveals some similarities. Among the common exploration criteria in the two deposits are Oligo-Miocene alkaline magma, mineralization depth of more than 300 meters, northeast trending structures, gold, arsenic and antimony geochemical association, presence of iron oxides such as jarosite and hematite, vuggy breccia textures, and silica and phyllic alteration hosting gold minerlization. The most important exploration criteria at the Dalli deposit, however, are Miocene chalk alkaline magmatism, depth of mineralization of more than 500 meters, strong potassic and phyllic alterations, presence of specularite mineral, northeast trending structures and strong high magnetic anomalies, associated with potassic alteration. Introduction Zagros orogenic belt and its geological subdivisions such as Urumieh-Dokhtar Magmatic arc (UDMA) and Sanandaj-Sirjan Zone (SSZ), as part of Alpine-Himalayan belt and product of Neogene closure of Neo-Tethys Ocean, host several large porphyry copper (Mo and Au) and epithermal gold deposits in Iran. Sari Gunay low sulfidation epithermal, Zarshuran sediment-hosted Carlin type and Dalli porphyry (Cu-Au) deposits are three major deposits in this belt. Several conceptual studies have been carried out on individual porphyry copper and epithermal gold deposits of this belt (e.g., Talesh-Hosseini et al., 2020; Ayati et al., 2012; Richards et al., 2006; Hezarkhani & Williams-Joins, 1998; Mehrabi et al., 1999). Nevertheless, limited studies have been conducted on the application of conceptual modelling in exploration (Daeijavad et al., 2020), and comparison of porphyry copper-gold and epithermal gold mineralizations. Therefore, the main objective of this research is to use earlier conceptual and description models of these deposits and, combining them with the results of this tudy, to identify various criteria for exploration across the two mentioned geological subdivisions of Zagros belt. Material and methods This study used geodynamic model of Zagros belt, detailed geological maps, remote sensing data, mineralogical and petrographic studies by electron microprobe and normal microscope, ICP geochemical analyses of more than 3500 surface soil samples, drill core data, 40Ar/39Ar age dating and fluid inclusion analyses at these deposits to characterize the controls on gold mineralization and to define exploration criteria for further exploration at Sari Gunay, Zarshuran, and Dalli, and other ones. Results Sari Gunay epithermal gold deposit is located in northwest of the SSZ and is associated with an alkaline magma. Geochemical analysis of surface and drill core samples show that gold mineralization at this deposit is associated with As, Sb, Hg, Tl, and Ag, with outer zones enriched in Pb, Zn, and Cu. Mineralization is hosted by strongly silicified subvolcanic fragmental rocks and diatreme breccias and dacite porphyritic rocks showing strong phyllic and argillic hydrothermal alterations, identified by remotely sensed image processing data. Iron oxide, orpiment, realgar and stibnite minerals are closely associated with gold mineralization in the altered fragmental host rocks of dacite-lithic tuff and brecciated dacite porphyry. Gold occurred as angstrom-size or solid solutions within arsenian pyrite rims over previously formed barren brassy pyrite. Rare amounts of native gold noted within the late quartz, brassy pyrite, and galena veins. Ar/Ar and K/Ar age dating and whole rock geochemical analyses showed that mineralization at Sari Gunay occurred at about 11 Ma (Oilgo-Miocene). Zarshuran is located in the north Takab geothermal basin in northwest Iran. This deposit is geologically located at the contact of the SSZ and the UDMA. The oldest rocks are Iman Khan schists, followed by Chaldagh limestone, Zarshuran black shale, and Qaradash shale. A Miocene brecciated and altered dacite porphyry and locally dacite lithic tuff intruded the Zarshuran black shale and Chaldagh limestone. Mineralization associated with silicification mostly occurred in the Zarshuran black shales and Chaldagh limestone and extended in a northwest direction. Ar/Ar and K/Ar age dating revealed that mineralization at Zarshuran occurred at about 14 Ma and was about the time of Miocene volcanic activities (13.7 ± 2.9 Ma). In Chaldagh limestone, gold mineralization is mostly concentrated in quartz veins. Quartz veins in Chaldagh limestone include barite, pyrite, arsenian pyrite, sphalerite, and iron oxides. Mineralized quartz veins and jasperoid lenses in the Zarshuran black shale contain arsenic-antimony sulfides, pyrite, gold-bearing arsenian pyrite, and base metal sulfides such as galena and sphalerite. Mineralization showed elements association of Au, As, Sb, and Pb. Dalli is a newly discovered porphyry Cu-Au deposit, which is located in the western margin of UDMA, near the contact the SSZ. Discovery of Dalli was initially based on alteration mapping by satellite imagery data, and then by using surface soil and rock geochemical studies, geological mapping, and magnetic surveys, which delineated two porphyry centers as targets for detailed geochemical prospecting. These porphyry centers (South Hill and North Hill), crop out within a northeast trending corridor of altered Oligo-Miocene dioritic plutonic rocks intruded into volcanic rocks. Dalli is a gold-rich porphyry Cu deposit in Iran, with proven reserve of 5 million tons of ore containing 0.65 g/t Au and 0.5% Cu. Mineralization is hosted by altered porphyritic amphibole-bearing diorite and occurs in quartz-hematite-magnetite stock works and veins. Hypogene mineralization is characterized by chalcopyrite, pyrite, bornite, magnetite, and native gold. Mineralization showed a strong element association of Cu, Au, and Fe. Chalcopyrite and rare hypogene bornite occur as dissemination in subvolcanic rocks and in quartz-chalcopyrite-pyrite-magnetite veinlets within potassic and phyllic alteration zones. Gold is observed as free grains and inclusions in pyrite and chalcopyrite. Supergene mineralization in the oxidized zone includes malachite, azurite, cuprite, and iron oxides, with limited supergene Cu enrichment characterized by covellite and chalcocite. The dioritic plutonic and andesitic volcanic host rocks were subjected to intense potassic (quartz-biotite-magnetite) and phyllic (quartz-sericite-chlorite) alterations. Discussion Mineralizations at Sari Gunay and Zarshuran, despite their different host rocks, show significant similarities, while, mineralization at Dalli is quite different. Dalli only shows some similarities with deep-seated low grade porphyry Cu-Au portion of the Sari Gunay mineralization. Exploration criteria, to search for similar deposits such as Sari Gunay and Zarshuran, are alkaline Oligo-Miocene magmatism, original mineralization depth of more than 300 meters, within a temperature range of 150 °C to 360 °C, NE-trending structures, Au-As-Sb-Hg-Tl-Te geochemical suit elements and related minerals, invisible gold in arsenian pyrite, strong silicification and widespread sericite-argillic alterations. Whereas, exploration criteria to search for Cu-Au porphyry deposits, like Dalli, are calk-alkaline Miocene dioritic magmatism, strong silicification and potassic alteration associated with Cu-Au mineralization and widespread surrounding propyllitic alteration associated with Mn-Zn mineralization, northeast and north trending structures, visible micro-sized native gold in quartz and chalcopyrite as well as strong magnetic anomalies associated with potassic alteration.

Keywords

• gold mineralization
• sari gunay
• dalli
• zarshuran
• exploration criteria