U-Pb and 40Ar-39Ar Geochronology and Isotopic Constraints on the Genesis of Copper-Gold-Bearing Iron Oxide Deposits in the Hasancelebi District, Eastern Turkey

Abstract

The Hasançelebi deposit in eastern Turkey, with proven reserves of 95 million metric tons, is a coppergold−bearing iron oxide deposit. It is chiefly hosted by rocks that underwent widespread sodic-calcic and potassic styles of alteration. In the Hasançelebi district, pervasive Na-Ca and K-Fe alteration types are overprinted by sericitization and by late alteration that occur in multiple, overprinting systems. The age of hydrothermal alteration and mineralization (ca. between 74−68 Ma) overlaps with the age of alkaline magmatism in the Hasançelebi district. Crystallization and cooling of alkaline magmatism is associated with hydrothermal features that spanned the duration of the district's igneous history. The 40 Ar/ 39 Ar and U-Pb geochronology of magmatism indicate that the hydrothermal system was synchronous with diabase and syenite and/or microsyenite porphyry intrusions and consisted of several discrete phases of Na-Ca and K-Fe alteration. The oldest alteration (phase 1) formed at ca 74.4 to 74.3 Ma; it is spatially and temporally associated with the emplacement of diabase dikes and contains scapolite and phlogopite. The next younger alteration (phase 2) formed at about 71.3 Ma and is spatially and temporally associated with syenite porphyry and microsyenite porphyry intrusions. It consists of scapolite , garnet, pyroxene, and actinolite that are superimposed on the first alteration phase. The next alteration assemblage (phase 3) formed at about 68.6 Ma and consists of phlogopite 2 and magnetite mineralization. Still later alteration (phase 4) overprints phases 1, 2, and 3 and consists of sericite-quartz, chalcopyrite, hematite, calcite, fluorite, and barite. Oxygen (δ 18 O) and hydrogen (δD) isotope analyses were carried out on phlogopite, sericite, barite, calcite, fluorite, and quartz representing the mineral assemblage formed during phases 1 and 4 of the hydrothermal alteration. The calculated δ 18 O(H 2 O) and δD(H 2 O) composition of the fluids that formed preore K-Fe alteration and postore alteration of phase 4 range between 15.1 to 8.5 and −124 to −85.6 per mil, respectively, and partially overlap the range for traditional magmatic waters. Oxygen and H isotope compositions from alteration minerals highlight two major points: Na-Ca and K-Fe alteration assemblages are likely derived from hightemperature primary magmatic fluids, and late sericitization is likely derived from fluids exsolved from cooling alkaline plutons during hydrothermal fracturing and consequent degassing at moderate temperatures. The initial εNdi values of the alteration zones range from −2.02 to −2.08, close to the calculated εNd value of associated syenite porphyry at the time of alteration (εNd (68.64Ma; −1.9). Nd-Sr isotope compositions combined with 40 Ar-39 Ar and U-Pb geochronology of the associated alteration suggest that the fluids were sourced from coeval diabase dikes and syenite porphyry and/or microsyenite porphyry intrusions. The rare earth element characteristics, 40 Ar-39 Ar and U-Pb geochronology of alteration and fr...

Late Cretaceous to Middle Eocene Magmatism and Metallogeny of a Portion of the Southeastern Anatolian Orogenic Belt, East-Central Turkey

“…3e-g). 4a, b), whereas another syenite porphyry has a younger U-Pb age of 71.27 ± 0.29 Ma (Kuşcu et al, 2011). The syenitic rocks and syenite porphyry yielded zircon U/Pb ages between 75.3 ± 0.4 and 75.7 ± 0.5 Ma (Table 3; Fig.…”

“…5a) suggests a minimum age for that hydrothermal system. 3c) whereas phlogopitic biotite and K-feldspar from Hasancelebi yielded ages of 74.26 ± 0.45 and 70.48 ± 0.42 Ma, respectively (Kuşcu et al, 2011). 5b).…”

“…2) with reserves of 94.8 Mt at 23% Fe 3 O 4 (Yuce et al, 2005), with local grades up to 1.9 wt % Ni, and 0.04 to 2 g/t Au (Ay et al, 2005) (Fig. This suite intruded into a Late Cretaceous alkaline volcanic and volcaniclastic rock sequence composing the extension-related Hekimhan basinal sequence (Kuşcu et al, 2011). The district contains two separate deposits-Hasancelebi to the east, and Karakuz to the west.…”

“…2). The deposits are hosted mainly by trachytic and syenitic rocks, and are associated with a pervasive sodic-calcic alteration assemblage consisting mainly of scapolite ± actinolite overprinted by a potassic alteration assemblage composed of phlogopitic biotite and magnetite (Kuşcu et al, 2011). Both deposits are associated with a magmatic suite containing syenite and syenite porphyry, trachytic to trachyandesite rocks, and diabase dikes.…”

“…Magmatic events at Hasançelebi are constrained by 40 Ar/ 39 Ar ages of biotite and U/Pb ages of zircon from syenite porphyry. Kuşcu et al (2011) also reported a 40 Ar/ 39 Ar biotite age of 76.84 ± 0.67 Ma for the trachytic rocks-the oldest rock in the Hasancelebi district, a 40 Ar/ 39 Ar hornblende age of 74.40 ± 0.51 Ma for a diabase dike that intruded the trachytic rocks, and a 40 Ar/ 39 Ar age of 74.32 ± 0.40 Ma for hydrothermal biotite from the same diabase dike (Table 3). 4a, b), whereas another syenite porphyry has a younger U-Pb age of 71.27 ± 0.29 Ma (Kuşcu et al, 2011).…”