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The Çöpler epithermal Au deposit and related subeconomic porphyry Cu-Au mineralised system is located in east-central Turkey, 120 km west of
the city of Erzincan, in Erzincan Province, 40 km east of the iron-mining city of Divriği, 550 km east of Ankara, and ~3 km
SE of the Euphrates River.
(#Location: 39° 25' 35"N, 38° 32' 4"E)
Gold and silver mining that dates back at least to Roman times, and possibly earlier is known in the district, with historic bullion production estimated at ~1.6 tonnes of gold. A copper-rich slag pile of ~25 000 tonnes is located at the western edge of the district and is believed to be waste from ancient bullion production. Modern gold production at the Çöpler mine commenced in 2010 as a heap leach operation producing an average of 19 500 tonnes per day. ToJanuary 1, 2015 over 29 Mt of oxide ore at an average grade of 1.66 g/t Au has been delivered to the heap leach pad for gold recovery.
The Çöpler deposit is hosted by the Eocene Çöpler-Kabatas magmatic complex, located within the Anatolian Plate, separating the Eurasian plate to the north, from the African/Arabian Plate to the south. It lies near the northern margin of a complex collision zone lying between the Pontide Belt/North Anatolian Fault (separating the Eurasian and Anatolian plates) and the East Anatolian Fault (separating the the Arabian and Anatolian plates). The region underwent crustal thickening related to the closure of a single ocean, or possibly several oceanic and micro-continental realms, in the late Cretaceous to early Tertiary.
The deposit is centred on a Mid-Eocene composite diorite to monzonite porphyry stock intruded into metasediments and limestone-marbles of the Permian Munzur Formation, part of the Late Palaeozoic to Mesozoic metamorphosed sedimentary basement. The enclosing lower Permian, limestone turbidite sequence has been metamorphosed to metasediments and is overlain by massive porcellanous limestone that has been altered close to the intrusion by both contact metamorphism and hydrothermal solutions.
The Çöpler intrusion is a hornblende quartz diorite porphyry that has undergone strong argillic alteration. The least altered diorite porphyry contains well-preserved hornblende, biotite and K feldspar phenocrysts set in a granular matrix of plagioclase and quartz with prominent magnetite. Flow alignment of the hornblende phenocrysts are observed locally. Gradational transitions to argillically-altered rock are evident on a centimetre scale in outcrop and drill core.
There may be several intrusive phases that have been obscured by alteration, comprising either potassic in the porphyry core or argillic and advanced argillic in association with the epithermal mineralisation. Eocene conglomerates on the northeastern side of the deposit show a similar style of alteration and therefore may predate mineralisation.
The primary control on the location of the Çöpler intrusion is interpreted to have been the metasediment-carbonate contact, although the intrusive outline has a roughly rectilinear shape, suggesting control by pre-existing ENE faulting, and a set of NNW trending fractures. The NNW striking bedding may also have influenced emplacement locally in the central part of the intrusion, where many intrusive contacts are parallel to bedding with a sill-like morphology, although it is likely that this also reflects the NNW trending fracture control.
The potassic-altered core of the porphyry system corresponds to a pronounced ground magnetic anomaly that has been modelled as a stock-like intrusion dipping steeply towards the south. In addition, there are a number of dykes and intrusive apophyses, most notably, a brecciated and strongly clay-altered intrusion centred on what is known as the Manganese Mine Zone on the northeastern section of the deposit.
Two parallel ENE striking structures, the Çöpler North and Çöpler South faults, which are ~300 to 500 m apart, and parallel to the elongation of the mineralised zone, cross the deposit area. They transect all rock units in the deposit area and may have provided the locus for the intrusive events. The Çöpler North fault is a low angle thrust fault passing through the Manganese Mine Zone, although it can only be traced for 200 m to the WSW, where it disappears in the marble where it parallels bedding. The Çöpler South fault is a high-angle structure forming the metasediment/marble contact, and can be traced to the ENE through the northern part of the Marble Contact Zone. Northeast and northwest striking faults exist between the two major structures reflecting the regional stress field that provided further ground preparation for hydrothermal mineralisation.
At least three jasperoid bodies occur along the Çöpler South Fault, and ground preparation for both the eastern stockwork quartz veinlet
zone (in the metasediment) and the western stockwork quartz veinlet zone (in diorite porphyry) is most likely related to the same fault. Numerous other small jasperoid bodies are related to an east-west lineament that intersects the Çöpler fault. At least one other fault occurs sub-parallel to the Çöpler North Fault, controling manganese mineralisation approximately 1 km to the NE. Copper oxide mineralisation in granodiorite porphyry and quartz monzonite porphyry in the NW corner of the deposit appears to be related to shear zones with this northwesterly trend.
The main ENE-WSW elongated intrusive is exposed over an area of 1700 x 1100 m within the main central section of the deposit, although diorite intrusives that do not outcrop also occur below the Manganese Mine and Marble Contact Zones, both on the eastern end of the mineralised zone. The mineralisation within these latter zones is proximal to and associated with the diorite intrusives. Additional contact metamorphic rocks in the form of jasperoids occur locally at contacts between the intrusives and calc-silicates.
Weathering has resulted in oxidation of the mineralisation close to surface. The oxidised cap is underlain by primary and secondary sulphide mineralisation. In addition to the economic gold-silver-copper, arsenic, lead, magnesium, manganese, mercury and zinc are also present.
Epithermal gold mineralisation occurs within structurally-controlled zones of stockwork and sheeted veins hosted by the Eocene diorite intrusive and an older
metasediment complex, and as contact-type mineralisation along the intrusive-metasediment fault contact with the Munzur Formation limestones. The epithermal
mineralisation may be related to porphyry copper-style mineralisation recognised in association with the intrusions.
Five main styles of gold mineralisation are recognised at Çöpler:
i). Stockwork quartz veining within metasedimentary rocks and diorite with disseminated marcasite, pyrite, arsenopyrite and tennantite-tetrahedrite. Oxidation produced goethitic/jarosite assemblages hosting fine-grained gold. This style occurs in the Main Zone.
ii). Clay-altered, brecciated and carbonate-altered diorite with rhodochrosite veinlets and disseminated marcasite, pyrite, realgar, orpiment, tennantite-tetrahedrite, other sulphosalts, sphalerite and galena, which occurs in the Manganese Mine Zone.
iii). Massive marcasite-pyrite replacement bodies along marble and faulted contacts, found in the Main Zone, Main Zone East, Main Zone West, Marble Contact Zone, West Zone and Manganese Mine Zone.
iv). Massive jarositic gossan, which occurs in the Marble Contact Zone and Main Zone Contacts.
v). Massive manganese oxide, as found in the Manganese Mine Zone.
Oxidation of these mineralisation types has resulted in gossans, massive manganese oxide and goethitic/jarositic assemblages hosting fine-grained free gold.
Six separate ore zones have been delineated at Çöpler, as follows.
• Main Zone, which lies in the central to west portion of the deposit area and covers an area of ~750 m north to south by 1000 m east to west. Typically mineralisation occurs from the surface to >200 m depth. Epithermal veinlets containing disseminated quartz-pyrite-arsenopyrite are primarily hosted in diorite and metasediments with some marble mineralisation on the eastern margin. Oxide mineralisation occurs from near surface to depths of ~40 m, with the thickest development over ridges and thinning in the intervening valleys. Minor volumes of massive sulphide pyrite mineralisation are also found.
• Manganese Mine Zone, occupies the eastern end of the deposit area, and is ~650 m wide from north to south, by ~650 m east to west. Prior to mining the surface expression was predominately of marble, although a moderate sized intrusion of diorite has been encountered sub-surface. A large part of the Manganese Mine Zone mineralisation occurs along the contact between the diorite and marble, occurring from the surface to ~400 m depth. Free gold occurs in the marble with minimal associated sulphides. Disseminated quartz-sulphide mineralisation occurs in clay-altered and brecciated diorites as well as locally carbonate-altered diorite. Moderate amounts of massive sulphide pyrite mineralisation is also found within the Manganese Mine Zone. The 'leachable' mineralisation occurs to a depth of > 200 m as a combination of free gold in marble and supergene oxidised mineralisation in both marble and diorite.
• Main Zone East, which represents the section of the resource that lies between the Manganese Mine Zone and Main Zone. The area is typified by narrow, weakly to moderately-mineralised gossans developed at the contact between the basement metasediments and the overlying marble. It is suggested that the gossan were produced from sulphides sourced from the diorite in the Manganese Mine Zone, and were emplaced along the metasediment marble contact as the diorite has crystallised.
• Marble Contact Zone occurs in the southeastern section of the deposit area, and is associated with a NE-striking fault contact between marble on the east and metasediments and intrusives to the west. It is typified by large 'plugs' of gossan and diorite that have formed at the junctions of large scale faults, which have focussed considerable mineralising fluid flow. The Marble Contact Zone is ~350 m wide, with an ENE strike length is 300 m. Mineralisation is found from surface to ~160 m, and occurs as both disseminated sulphides in veinlets and massive sulphide along the marble contact. Oxidation occurs to greater depths than in the Main Zone.
• West Zone, which occupies the westernmost portion of the deposit area and is located at the contact between the basement metasediments and the overlying limestone, where a large scale NE-trending fault is located. Mineralisation occurs within veinlets containing disseminated sulphides, massive sulphide and oxidised gossan. It has a strike length of ~700 m in a northeasterly direction and is ~150 m wide. Multiple narrow mineralised zones occur sub-parallel to the faulted contact and are found to a depth of ~150 m below surface.
• Main Zone West, that is located in the NW corner of the project area, at the contact between diorite, marble and the basement metasediments. Mineralisation is hosted within narrow gossans located at the contact and in sub-parallel veinlets containing disseminated sulphides within the marble and metasediments. It has a strike length of ~750 m and is ~75 m wide.
Resources and Reserves
NI 43-101 compliant mineral resources at 31 December, 2015 (Alacer Gold website, 2016) were:
Oxide ore at a variable cut-off
Measured + indicated resource - 30.009 Mt @ 1.05 g/t Au, 3.08 g/t Ag, 0.16% Cu,
Inferred resource - 16.524 Mt @ 1.05 g/t Au, 3.08 g/t Ag, 0.16% Cu,
Sulphide ore at 1.0 g/t Au cut-off
Measured + indicated resource - 85.688 Mt @ 2.02 g/t Au, 5.14 g/t Ag, 0.11% Cu,
Inferred resource - 25.059 Mt @ 1.91 g/t Au, 10.66 g/t Ag, 0.16% Cu,
Measured + indicated resource - 115.698 Mt @ 1.77 g/t Au, 4.60 g/t Ag, 0.12% Cu, (204 t of contained Au),
Inferred resource - 41.583 Mt @ 1.51 g/t Au, 8.01 g/t Ag, 0.13% Cu, (62.5 t of contained Au).
NI 43-101 compliant ore reserves (included within resources) at 31 December, 2015 (Alacer Gold website, 2016) were:
Proved + probable reserve - 58.884 Mt @ 2.15 g/t Au, 5.44 g/t Ag, 0.11% Cu.
This summary is drawn from "Bohling et al., 2015 - Feasibility Update, Çöpler Sulfide Expansion Project, Erzincan Province, Turkey; an NI 43-101 Technical Report prepared byAlacer Gold Corp. with contributions from Jacobs Minerals, Inc., Golder Associates Inc., SRK Consulting (U.S.), Inc., Amec Foster Wheeler E&C Services Inc. (Amec Foster Wheeler), Metallurgium, Optiro Pty. Ltd., and Global Resource Engineering. 411p."
The most recent source geological information used to prepare this summary was dated: 2015.
This description is a summary from published sources, the chief of which are listed below.
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