Ali Imer | University of Alberta (original) (raw)

Papers by Ali Imer

Tectonomagmatic Influences on Metallogeny and Hydrothermal Ore Deposits: A Tribute to Jeremy P. Richards (Volume I)

Palaeogeography, Palaeoclimatology, Palaeoecology, 2020

Geochimica et Cosmochimica Acta, 2016

Mineralium Deposita, 2014

Mineralium Deposita, 2012

Earth and Planetary Science Letters, 2016

Palaeogeography, Palaeoclimatology, Palaeoecology, 2020

Keywords: neotectonics lithospheric structure strike-slip fault structural geology geochemistry A... more Keywords: neotectonics lithospheric structure strike-slip fault structural geology geochemistry Australia The interior of the Australian continent shows evidence for late Quaternary to Recent fault-controlled mantle 3 He and CO 2 degassing. A series of interconnected NW-striking sinistral faults, the Norwest fault zone (NFZ), in south-central Australia are associated with travertine mounds, the latter show a regular spacing of 50–70 km. U-series ages on 26 samples range from 354 ± 7 to 1.19 ± 0.02 ka (2σ errors) and suggest a clustering every ∼3–4 ka since ∼26 ka. Geochemical data demonstrate a remarkable mantle-to-groundwater connection. Isotopic data indicate that the groundwater is circulating to depths >3 km and interacting with Neoproterozoic/Cambrian basement and mantle volatiles. 3 He/ 4 He isotope ratios show that the He comes in part from the mantle. This demonstrates that the NFZ cuts through the entire crust and provides pathways for mantle degassing. Scaling relationships suggest that the series of sinistral faults that make up the NFZ are interconnected at depths and have a significant strike length of 60–70 km or more. The NFZ occurs where a major compositional boundary and a significant heat flow anomaly occurs, and a major step in lithospheric thickness has been mapped. We discuss a tectonic model in which recent stress field, heat flow and lithospheric structure in central Australia reactivated a set of steeply dipping Neoproterozoic faults, which may now be growing into a crustal/lithospheric-scale structure.

The Çöpler Au deposit (measured and indicated resource of 122.8 million tonnes at 1.7 g/t Au, 4.8... more The Çöpler Au deposit (measured and indicated resource of 122.8 million tonnes at 1.7 g/t Au, 4.8 g/t Ag, and 0.1 wt % Cu) is centered around shallow-level dioritic to granodioritic intrusive rocks of the middle Eocene Çöpler-Kabatas¸magmatic complex, which have been emplaced into a succession of regionally metamorphosed late Paleozoic-Mesozoic sedimentary and carbonate rocks. The deposit comprises a centrally located subeconomic porphyry Cu-Au system characterized by a potas-sically altered (biotite-K-feldspar-magnetite) core overprinted by a more extensive phyllic (quartz-sericite) alteration zone. The potassic alteration zone is associated with early M-type hairline magnetite and crosscutting B-type quartz ± magnetite ± sulde veinlets, whereas the enveloping phyllic-altered rocks contain abundant D-type quartz-pyrite and lesser polymetallic quartz-sulde veinlets. Intermediate-suldation epithermal Au mineralization that overprints the porphyry occurred in two stages. Main-stage epithermal mineralization is characterized by carbonate sulde veinlets consisting of manganocalcite, arsenical pyrite, arsenopyrite, marca-site, chalcopyrite, tennantite/tetrahedrite, galena, and sphalerite. Late-stage sooty pyrite veinlets contain some realgar and orpiment and are associated with zones of extensive carbonate alteration. In the carbonate sulde veinlets, invisible gold is primarily hosted within arsenical pyrite and, to a lesser extent, by arsenopyrite, tetra-hedrite, and tennantite. In sooty pyrite veinlets, invisible gold is associated with ne-grained arsenical pyrite. Manto-type carbonate-replacement zones occur in the distal portions of the porphyry system and constitute a signicant gold resource. These carbonate-replacement bodies display a mineral paragenesis similar to that of the epithermal carbonate sulde veinlets in that they contain abundant arsenical pyrite together with lesser chalcopyrite, arsenopyrite, and marcasite, and sparse sphalerite, galena, tennantite, and tetrahedrite. Invisible gold in these ores is contained mainly within pyrite and chalcopyrite and, to a lesser extent, in arsenopyrite, tetrahedrite, and tennantite. Polyphase brine inclusions (~47–62 wt % NaCl equiv) in early B-type quartz ± magnetite ± sulde vein-lets were trapped together with low-salinity (~3–5.5 wt % NaCl equiv), vapor-rich inclusions at temperatures ~390°C and at a depth of ~1.5 km under lithostatic conditions. Fluids associated with the overprinting phyllic alteration were slightly cooler (~370°C) and less saline (37–42 wt % NaCl equiv). Fluid inclusions in man-ganocalcite and sphalerite from epithermal carbonate sulde veinlets trapped moderate-salinity (4–15 wt % NaCl equiv) uids at ~290°C, whereas uid inclusions hosted in barite and realgar from sooty pyrite veinlets were formed from low-temperature (~100°C) and low-to moderate-salinity (1–14 wt % NaCl equiv) uids. These data indicate that the Au-mineralizing system at Çöpler progressed from a high-temperature porphyry system to a relatively low temperature, intermediate-suldation epithermal system. Deposition of gold in the early stages of epithermal mineralization resulted from cooling, suldation, and neutralization of predominantly magmatic sourced hydrothermal uids, whereas a meteoric water component is evident in the latest stage of mineralization. Deposit-scale geologic observations combined with uid inclusion and stable isotope evidence suggest that mineralization at Çöpler records activity of a relatively deep epithermal system and that its formation was structurally and lithologically controlled. Specically, the thick, premineralization carbonate sequence once overlying the deposit acted as a pressure seal and also as a neutralizing agent during the build up of the mag-matic-hydrothermal system. The weakening of this carbonate cover by igneous intrusion and subsequent hydro-thermal activity may have contributed to later selective erosion of the alteration zone, thereby telescoping the intermediate-suldation epithermal system onto the earlier porphyry system and creating the Çöpler window.

Vein and breccia carbonates precipitated in a highly fractured/faulted carbonate bedrock in SW Tu... more Vein and breccia carbonates precipitated in a highly fractured/faulted carbonate bedrock in SW Turkey were investigated through high-resolution U-series geochronology, microstructural and geochemical studies including C–O–Sr isotope and rare-earth element and yttrium (REY) analyses. Petrographical observations and geochronological data are interpreted as evidence that the calcite veins formed through a crack-seal mechanism, mostly accompanied/initiated by intensive hydraulic fracturing of the host limestone in response to high-pressure fluids, which is manifested by multi-stage breccia deposits. Microscale U-series dates (272.6–20.5 kyr) and geochemical compositions of the vein/breccia samples provide information on the timing and mechanism of the vein formation and identify the source of CO2-bearing fluids responsible for the carbonate precipitation. d 18 O VPDB and d 13 C VPDB values of the calcite veins range between À5.9 and À1.7‰, and À10.6 and À4.6‰, respectively. The isotopic compositions of the veins show highly fluctuating values as calcite grew successively perpendicular to vein walls, which, in combination with microstructural and geochronological constraints, are interpreted to reflect episodic CO2 degassing events associated with seismic and aseismic deformation. Oxygen and Sr isotope compositions (d18O VPDB : À5.9 to À1.7‰; 87Sr/86Sr: 0.7082 to 0.7085) together with REY concentrations indicate deep infiltration of meteoric waters with various degrees of interactions mostly with the host limestone and siliciclastic parts of the basement rocks. Oxygen and carbon isotope compositions suggest CO 2 degassing through intensive limestone dissolution. While majority of the veins display similar Post-Archaean Australian Shale (PAAS)-normalised REY variations, some of the veins show positive Eu PAAS anomalies, which could be indicative of contributions from a deeply derived, heated, and reduced fluid component, giving rise to multiple fluid sources for the calcite veins. Vein calcite formed in fault-induced fractures offers insights into structural features, genetic characterisation of the parental fluids, and late Quaternary degassing of subsurface CO2 accumulations.

Tectonomagmatic Influences on Metallogeny and Hydrothermal Ore Deposits: A Tribute to Jeremy P. Richards (Volume I)

Palaeogeography, Palaeoclimatology, Palaeoecology, 2020

Geochimica et Cosmochimica Acta, 2016

Mineralium Deposita, 2014

Mineralium Deposita, 2012

Earth and Planetary Science Letters, 2016

Palaeogeography, Palaeoclimatology, Palaeoecology, 2020

SEG Special Publications v. 24 - Tectonomagmatic Influences on Metallogeny and Hydrothermal Ore Deposits: A Tribute to Jeremy P. Richards, 2021

Öksüt is a breccia-hosted high-sulfidation epithermal gold-copper deposit, situated within the De... more Öksüt is a breccia-hosted high-sulfidation epithermal gold-copper deposit, situated within the Develidag Volcanic Complex in south-central Anatolia. The volcanic complex, exposed on the northern edge of the Tauride range, is largely made up of late Miocene andesitic to dacitic porphyries, covered by a succession of Pliocene basalts and basaltic andesites. A series of N-S-to NNW-trending faults of the regional central Anatolian fault zone partly cut and border the volcanic complex to the east and west. Mineralization at Öksüt follows a predominant north-northwest trend that correlates well with the regional stress regime. The bulk of the mineralization occurs in two domains, the Keltepe and Güneytepe orebodies, where steeply dipping and pervasively supergene oxidized breccia zones exploited funnel-shaped diatreme conduits within pyroxene andesite porphyry. Emplacement of these phreatomagmatic breccias was largely controlled by vertical to subvertical faults with dominant normal-slip components. Mineralized breccias comprise a central zone of residual vuggy to massive silica alteration, laterally and vertically grading into zones of quartz-alunite and quartz-alunite-clay alteration. These silica-altered breccias contain relatively high gold grades, whereas significant mineralization was also encountered in quartz-alunite-clay alteration. In the oxide zone, gold occurs in native form, whereas in the hypogene zone it occurs both as native gold or within pyrite-enargite accompanied by marcasite, and rare chalcopyrite and tetrahedrite. To the west of Keltepe and in Güneytepe, at depth, the altered and mineralized breccias pass into barren zones of argillic and then into biotite-magnetite ± K-feldspar ± anhdyrite alteration, the latter typical of porphyry-type systems. Sporadic zones of calc-silicate alteration, represented by grossularite, diopside, and vesuvianite, are also present. Three 40 Ar/ 39 Ar ages obtained from alunite and illite range between 5.7 to 5.5 Ma and are concordant with previously reported U-Pb and 40 Ar/ 39 Ar ages (~6-5.5 Ma) from host pyroxene andesite porphyry. This suggests that high-sulfidation alteration and mineralization developed contemporaneously with postsubduction magmatism at the Develidag Volcanic Complex, in relationship to regional E-W-directed extension that commenced at ~6 Ma. Our new ages also confirm Öksüt as the youngest epithermal gold deposit discovered to date in Anatolia, and possibly in the entire Western Tethyan metallogenic belt. The topographic prominence of the volcanic edifice combined with high permeability of the breccias favored deep supergene sulfide oxidation, thereby rendering Öksüt economically viable. Gold encapsulated in hypogene sulfides was liberated during the oxidation, whereas the copper was leached to produce a discontinuous chalcocite-and covellite-dominated enrichment zone, up to 50 m thick, at the base of oxidation.

SEG 100 Conference: Celebrating a Century of Discovery, 2021

The Turkish part of the Mesozoic-Cenozoic Western Tethyan Metallogenic Belt contains a large numb... more The Turkish part of the Mesozoic-Cenozoic Western Tethyan Metallogenic Belt contains a large number of epithermal systems mainly clustered in western and northeastern Anatolia. The Gicik gold deposit is located within a rather unexplored section of this belt in north central Anatolia, about 15 km north of Ankara city center. Gold mineralization is hosted in middle Eocene agglomerates and massive to flow-banded andesite to dacite lavas overlying the Variscan basement of the southern margin of the Laurasian Sakarya Zone. Volcanic rocks are medium-K, calc-alkaline in character and show relative depletions in high field strength elements and relative enrichments in large-ion lithophile and light rare earth elements. These characteristics indicate that middle Eocene magmatism at Gicik was developed in a subduction-related setting.

Gold mineralization occurs in a series of NNE-trending, vertical to subvertical siliceous veins (up to 10 meters thick), which have been localized along dextral reverse faults. Fault plane measurements indicated two distinct fault sets: the first oriented NE-SW and hosting the mineralized veins and the second set oriented in NW-SE to E-W, offsetting the mineralized structures. According to the paleostress analyses of fault-slip data, vein-hosted gold mineralization was interpreted to have developed under NW-directed transpression.

Widespread hydrothermal alteration is characterized by vein-proximal silicification consisting of chalcedony/fine-grained massive to colloform-banded quartz to coarser-grained gray quartz as well as late
amethystic quartz, surrounded by wider zones of argillic alteration represented by quartz-illite-kaolinite assemblages. District-scale propylitic alteration, characterized by chlorite-epidote-carbonate-quartz-pyrite assemblages, envelops the aforementioned alteration domains.

Siliceous veins display typical textures of low-sulfidation epithermal systems including colloform banding, hydrothermal brecciations, stockwork veinlets, and lattice-bladed textures. Mineralized samples from the surface have been extensively oxidized into hematite and goethite. Relatively fresh exposures along steep valleys, however, contain hypogene sulfide phases including pyrite, arsenopyrite, and Ag tetrahedrite together with native gold. Supergene covellite and digenite locally overprints Ag tetrahedrite hosted in colloform banded veins. Electron microprobe analysis revealed that significant concentrations of gold and silver (up to ~700 ppm and ~8.5 wt %, respectively) are contained within sulfide/sulfosalt minerals.

K-Ar and Ar/Ar dating of igneous and hydrothermal minerals suggest that volcanic activity and epithermal-style alteration occurred contemporaneously at ~44 Ma during the terminal stages of widespread
Paleogene volcanism in north central Anatolia. This period of volcanism is considered to have been triggered either by collisional processes or by breakoff of the downgoing northern Neotethyan slab following collision between Sakarya Zone and the Tauride-Anatolide Block. Overall deposit characteristics of the Gicik low-sulfidation epithermal system are analogous with similarly aged gold deposits of the collisional belt located in Biga Peninsula and the eastern Pontides. Thus, we propose that middle Eocene tectonomagmatic conditions along the central Sakarya Zone were also favorable for generation of low-sulfidation
(and possibly intermediate-sulfidation) epithermal mineralization.