Search

Rapidly changing ore deposit types in the Late Cretaceous and early Tertiary in the Southeastern Anatolian orogenic belt in east-central Turkey, from Baskil on the south to Divrigi on the north, broadly reflect shifting tectonic environments in an evolving collisional orogen, a part of the extensive Tethyan orogen. Late Cretaceous (~83-79 Ma) subduction-related arc magmatism in the Baskil arc was followed by extension that exhumed the metamorphic basement, unroofed the obducted ophiolites, and filled basins with Maastrichtian to Paleocene subaerial and submarine sedimentary rocks. Calc-alkaline (Divrigi pluton, ~76-73 Ma) and alkaline igneous rocks (Hasançelebi and Keban districts, ~76-74 Ma) accompanied post-Baskil arc extension. In the early to middle Eocene, shallow and locally voluminous intrusions of intermediate composition (Çöpier, Kabatas, Bizmisen-Calti, Dedeyazi-Polat, Karamadazi, and Horoz), localized mainly along major strike-slip faults, formed during closure of the Neotethyan Ocean. These intrusions are dated between ~50 and 44 Ma, peaking at 48 Ma. Geochemical data from a suite of igneous rock samples across the transect reflect temporally based changes from arc-type to late orogenic environments, as demonstrated by Late Cretaceous rocks in the Baskil area on the south and the more deeply eroded Late Cretaceous plutons in the Divrigi area on the north (Divrigi). These magmatic products were followed in the Eocene by calc-alkaline magmatism related to either incipient slab-rupture or crustal-scale faults that cut from northeast (Çöpler, Kabatas, Bizmisen-Calti, and Polat-Cavuslu) to southwest (Karamadazi and Horoz) obliquely across the transect. The multielement patterns for the Late Cretaceous magmatic rocks resemble the patterns for magmas generated in enriched source regions compared to primitive mantle and mid-oceanic-ridge basalt. Locally, at Divrigi-Hasançelebi and Keban, the geochemical characteristics are suggestive of the influx of low field strength elements into the mantle source regions from a subducted slab, and an arc to postcollisional to late-orogenic setting for their generation. Eocene magmatic rocks display similar geochemical characteristics regardless of the geographic setting and associated hydrothermal system. Their characteristics favor a subduction zone enrichment that was inherited either from an older event, or from an older slab, or from a mantle wedge contaminated by a contemporaneous subduction component. 40Ar/39Ar and U/Pb geochronology on biotite, zircon, K-feldspar, hornblende, and sericite from a suite of magmatic rocks and alteration zones defines three magmatic-related metallogenic events in the Southeastern Anatolian orogenic belt between 78 and 44 Ma. The oldest metallogenic event between ~78 to 74 Ma is related to arc-type calc-alkaline magmatic rocks (83-79 Ma) intruded into the Bitlis-Poturge and Malatya-Keban meta-morphics and overlying Komurhan-Ispendere ophiolites of Tauride platform. Uneconomic porphyry-type Cu-Au systems formed at Topalkem-Baskil (Elazig) and Ispendere-Sisman (Malatya). A second metallogenic event, between ~74 and 69 Ma, is contemporaneous with postcollisional exhumation and extension-related magmatism. During this event, calc-alkaline followed by alkaline magmatism (76-73 Ma) was accompanied by formation of iron oxide copper-gold (IOCG) systems at ~74 to 73 Ma at Divrigi (Sivas). Alkaline magmatism at ~76 to 74 Ma is associated with IOCG systems at Hasançelebi (Malatya) and porphyry Cu-Mo and Pb-Zn veins at Keban (Elazig). The youngest metallogenic event between ~50 and 40 Ma is represented by porphyry Cu-Au deposits associated with calc-alkaline intrusive complexes at Çöpler and Kabatas and Fe skams at Karamadazi, Horoz, Dedeyazi, and Bizmisen-Calti. [ABSTRACT FROM AUTHOR]

The Mesozoic iron oxide-copper-gold (IOCG) subprovince of littoral south-central Perú, centered at latitude 15°11' S, longitude 75°6' W, incorporates Marcona, the preeminent central Andean iron oxide deposit (1.9 Gt @ 55.4% Fe), and Mina Justa, one of the few major Andean IOCG deposits with economic copper grades (346.6 Mt @ 0.71% Cu). The emplacement of magnetite orebodies with uneconomic Cu grades (avg 0.12%) at Marcona was controlled by northeast-striking faults transecting an active andesitic-dacitic, shallow-marine Middle Jurassic (Aalenian to Oxfordian) arc. In contrast, hypogene Cu sulfide (~1.5 g/t Ag, 0.12 g/t Au) mineralization at Mina Justa was emplaced along reactivated listric-normal detachment faults during the mid-Cretaceous inversion of the contiguous, plate boundary-parallel, Aptian to Albian Cañete basin, accompanied by the earliest, largely granodioritic-dioritic, stocks of the Coastal batholith. Alteration and mineralization assemblages, supported by 40Ar/39Ar geochronology of biotite, phlogopite, actinolite, cummingtonite, and K-feldspars, reveal a history of magmatic and hydrothermal processes extending episodically for at least 80 m.y., from ca. 177 to 95 Ma, wherein metal-rich mineralization events were preceded and separated by episodes of barren alteration. At Marcona, precursor, subocean-floor hydrothermal activity in the Aalenian (177 Ma) and Bajocian (171 Ma) generated, respectively, cummingtonite and phlogopite-magnetite assemblages through high-temperature Mg-Fe metasomatism of previously metamorphosed Lower Paleozoic Marcona Formation siliciclastic rocks and minor carbonate units underlying the nascent Río Grande Formation arc. Subsequent areally widespread, albite-marialite alteration (Na-Cl metasomatism) largely predated but overlapped with the emplacement of an eu echelon swarm of massive magnetite orebodies, in turn overprinted by subordinate magnetite-sulfide assemblages. Magnetite and weak Cu and Zn sulfide mineralization coincided with a 156 to 162 Ma episode of andesitic eruption and dacitic intrusion which terminated the growth of the arc, but was hosted largely by quartz-rich metaclastic rocks. From 162 to 159 Ma, iron oxide mineralization evolved from magnetite-biotite-calcic' amphibole ± phlogopite ± fluorapatite to magnetite-phlogopite-calcic amphibole-pyrrhotite-pyrite assemblages. These were overprinted at 156 to 159 Ma by chalcopyrite-pyrite-calcite ± pyrrhotite ± sphalerite ± galena assemblages, locally resulting in grades of 0.45 percent Cu and 0.5 percent Zn. Hydrothermal activity was thereafter focused in the Mina Justa area, 3 to 4 km to the northeast of Marcona, where Middle Jurassic andesites experienced intense albite-actinolite alteration at ca. 157 Ma, i.e., contemporaneous with sulfide mineralization at Marcona, and magnetite-microcline alteration (K-Fe metasomatism) at ca. 142 Ma. Development of the Mina Justa Cu (-Ag) deposit proper, however, began much later, with, successively, actinolitization at ca. 109 Ma, the deposition of calcite and specular hematite, now entirely pseudomorphed by magnetite, and the metasomatic emplacement of bodies of barren, massive magnetite and pyrite at 101 to 104 Ma. Finally, at 95 to 99 Ma, chalcopyrite-bornite-digenite-chalcocite mineralization, with abundant calcite and hematite, was emplaced as two ~400-m-long, ~200-m-wide, gently dipping, tabular arrays of breccia and stockwork, cored by preexisting magnetite-pyrite lenses. Supergene oxidation generated a chrysocolla-atacamite-covellite blanket, hosting ~40 percent of the Cu reserve, prior to the eruption of a 9.1.3 ± 0.25 Ma rhyodacitic ignimbrite flow. Although areally contiguous, the major magnetite and copper-rich centers of the Marcona district record independent metallogenic episodes widely separated in age.… [ABSTRACT FROM AUTHOR]

Four economic porphyry copper-gold deposits, Endeavour 22, 26, 27, and 48, occur within the Late Ordovician Goonumbla Volcanic Complex of central-west New South Wales, Australia. Together these deposits have a combined ore reserve of 63.6 million metric tons (Mt) at 1.1 percent copper and 0.5 g/t gold. Mineralization is centered in narrow, pipelike quartz monzonite porphyry (QMP} intrusive complexes. We have recognized at least nine intrusive phases within the Endeavour deposits. These are, in order of emplacement, as follows: a premineral equigranular monzodiorite; early-mineral, equigranular to weakly porphyritic biotite quartz monzonite (BQM) stocks and dikes, synmineral K-feldspar QMP (K-QMP} pipes and dikes; late-mineral augite-biotite-K-feldspar QMP (KA-QMP) intrusions and biotite QMP (B-QMP) dikes; and postmineral basaltic trachyandesite dikes, augite monzonite porphyry dikes, and basaltic dikes. Early-stage biotite-magnetite and propylitic alteration of the host volcanic rocks and K-feldspar alteration of the BQM occurred at each deposit during the intrusion of the BQM stocks and early-mineral B-QMP dikes. Transitional-stage unidirectional solidification textures and other related anisotropic textures formed mostly during the emplacement of K-QMP and KA-QMP intrusions. Main-stage sulfide mineralization at all four deposits is spatially and temporally associated with. the K-QMP and, to a lesser extent, KA-QMP intrusions and their associated K-feldspar and sericite-hematite alteration. assemblages, and is characterized by multiple generations of stockwork and sheeted quartz, K-feldspar, bornite, chalcopyrite, and gold-bearing veins. Late-stage sericite-quartz-copper-sulfide-carbonate-hematite alteration and vein assemblages formed. prior to the emplacement of the postmineral intrusions. Weak to moderate postmineral propylitic alteration assemblages were the last alteration event related to the QMP intrusive complexes. Intrusive... [ABSTRACT FROM AUTHOR]