Economic Geology
Pooya Seyed Salehi Naeini; Saeid alirezaei
Abstract
The Kharestan-Bidester area, northwest of the Taftan volcano, is covered by a series of Plio-Quaternary lava flows and pyroclastic materials. The area is marked by extensive silicic and argillic alterations. The silicic zones, distinguished by vuggy texture, are bordered by advanced-intermediate argillic ...
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The Kharestan-Bidester area, northwest of the Taftan volcano, is covered by a series of Plio-Quaternary lava flows and pyroclastic materials. The area is marked by extensive silicic and argillic alterations. The silicic zones, distinguished by vuggy texture, are bordered by advanced-intermediate argillic alterations. They occur as linear features across faults and fractures, as well as massive bodies of variable sizes, and are comparable, at regional scale, to lithocaps developed in the upper parts of the porphyry systems. The silicic-argillic zones are mineralized with gold at variable grades. Gold occurs mostly as submicroscopic particles of electrum and native gold. Pyrite, variably oxidized at surface and shallow levels, is the main metallic mineral, associated with trace sulfosalts, tetrahedrite and enargite. Minor malachite staining locally occurs in the ore zones. The geologic setting, hydrothermal alteration, ore mineralogy and texture/structure allow the Kharestan-Bidester to be compared with high-sulfidation epithermal systems.
Economic Geology
Maryam Emami Jafari; Saeed Alirezaei; Iraj Rasa; Jochen Kolb
Abstract
The Hired gold deposit in the Lut block, East Iran, is closely associated with an intermediate-mafic intrusive complex consisting of granodiorite to diorite, hornblende quartz-monzonite, and gabbro-diorite intruded into Eocene volcanic rocks. The intrusions are distinguished by high contents of CaO, ...
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The Hired gold deposit in the Lut block, East Iran, is closely associated with an intermediate-mafic intrusive complex consisting of granodiorite to diorite, hornblende quartz-monzonite, and gabbro-diorite intruded into Eocene volcanic rocks. The intrusions are distinguished by high contents of CaO, FeOt, and MgO, and rather low K2O+Na2O implying they crystallized from weakly differentiated magmas. This subject, and the relatively high Mg# (36.36 to 52.32) imply the involvement of a mantle source in the production of the parent magma. The intrusions are metaluminous, calc-alkaline to high-K calc-alkaline, and distinguished by the occurrence of ilmenite as an accessory mineral. Mineralization occurs in veins and veinlets disseminations in the granodiorite intrusion and the volcanic rocks, closely associated with tourmaline, silicic, and carbonate alterations, and is distinguished by abundant pyrrhotite, arsenopyrite, pyrite, and minor chalcopyrite, galena and sphalerite. Gold occurs mostly as submicroscopic grains in the pyrite and arsenopyrite. The mineralogical and geochemical attributes of the intrusive complex, and the ore mineralogy, allow the Hired to be classified as a gold deposit related to reduced I-type granitoids. The reducing nature of the parent magma can be explained by introduction of reduced crustal materials into the source area, and/or assimilation of carbonaceous metasedimentary rocks.
Petrology
Seyed Mohsen Kashfi; Saeed Alirezaei; Mohammad Reza Hosseini; Iraj Rasa
Abstract
The Zaghdareh area in the Esfandagheh-Faryab ophiolitic complex, southern Sanandaj-Sirjan belt, embraces extensive outcrops of mafic-intermediate lava flows and a felsic intrusive body. The volcanic rocks are calc-alkaline to tholeiitic, metaluminous, and distinguished by depletions in light rare earth ...
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The Zaghdareh area in the Esfandagheh-Faryab ophiolitic complex, southern Sanandaj-Sirjan belt, embraces extensive outcrops of mafic-intermediate lava flows and a felsic intrusive body. The volcanic rocks are calc-alkaline to tholeiitic, metaluminous, and distinguished by depletions in light rare earth elements and relatively flat patterns for heavy rare earth elements in chondrite-normalized diagram; the (La/Yb)N ratio is lower than unity for most samples. The chemical attributes for the Zaghdareh volcanic rocks are comparable to those developed in suprasubduction zones. The Zaghdareh intrusive body is distinguished by abundant plagioclase and quartz, and subordinate hornblende, phenocrysts in quartz-feldspar rich matrix. Representative samples from the intrusion plot in the trondhjemite-tonalite fields in the normative An-Ab-Or diagram. The intrusion is calc-alkaline to tholeiitic, peraluminous, and marked by enrichments in Na2O and CaO and depletions in K2O, Rb, and most other LILEs, as well as low K2O/ Na2O ratios, very low Rb/Sr ratio, and distinct depletions in light rare earth elements, which are typical of the oceanic plagiogranites. Results from this study and a comparison with other ophiolitic suites in Iran suggest that the occurrence of plagiogranites is a recurring feature associated with the development and evolution of ophiolitic suites in suprasubduction zones.
Economic Geology
Rasoul Sepehrirad; Saeid Alirezaei
Abstract
The Gazestan iron-apatite deposit in the Bafq mining district, is hosted in the upper Proterozoic-lower Cambrian volcanic-sedimentary sequence, known as Rizu series, and shallow intrusions. In backscattered electron (BSE) images, the apatite displays irregular light and dark zones with variable compositions. ...
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The Gazestan iron-apatite deposit in the Bafq mining district, is hosted in the upper Proterozoic-lower Cambrian volcanic-sedimentary sequence, known as Rizu series, and shallow intrusions. In backscattered electron (BSE) images, the apatite displays irregular light and dark zones with variable compositions. The dark zones contain inclusions of monazite and xenotime, and are distinguished by depletions in LREE+Y, Na and Cl, and enrichments in Ca and P. Development of reaction rims around apatite crystals, the occurrence of monazite and xenotime as scattered fine grains as well as filling microfractures in the dark zones, and the occurrence of the REE minerals at apatite-magnetite boundary provide evidence for alteration of the original apatite crystals in Gazestan. There is evidence that the apatite crystals formed during original magnetite-apatite ore formation, interacted and reequilibrated with fluids. During a coupled dissolution-reprecipitation process, the original apatite partially reacted with fluids of external origin. This led to leaching/reprecipitation of certain components, in particular the REEs, and development of dark apatite zones with fine, scattered monazite and xenotime grains, as well as the occurrence of fine REE mineral grains across microscopic fractures in apatite, calcite and quartz.
Economic Geology
Rasoul Sepehrirad; Saeed Alirezaei; Amir Morteza Azimzadeh
Abstract
The Gazestan magnetite-apatite deposit is hosted within an upper Proterozoic-lower Cambrian volcanic-sedimentary sequence, known as Rizu series, in the Bafq district, Central Iran. The Gazestan deposit occurred in intensely altered felsic-intermediate subvolcanic and volcanic host rocks. Field observations, ...
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The Gazestan magnetite-apatite deposit is hosted within an upper Proterozoic-lower Cambrian volcanic-sedimentary sequence, known as Rizu series, in the Bafq district, Central Iran. The Gazestan deposit occurred in intensely altered felsic-intermediate subvolcanic and volcanic host rocks. Field observations, drill core logging, petrographic studies, as well as geochemical and XRD data are indicative of differences in alterations assemblages and temporal/spatial distribution of the alteration products, compared to other iron oxide-apatite deposits in the Bafq district. Unlike many other Bafq district iron deposits, sodic alteration is only locally developed. Similarly, Ca+Fe or actinolitic alteration is poorly developed in Gazestan. Chloritic and sericitic alterations are most closely associated with ore formation in Gazestan. Chlorite commonly associated with magnetite, quartz and calcite in the altered host rocks. The chemical composition of chlorite falls in pycnochlorite and clinochlore fields. Calculated temperature for chlorite formation varies between 324-236 ºC. Sericite occurred both as a proximal alteration in ore zones, and as a distal alteration product in the volcanic and subvolcanic host rocks. Calcic-iron alteration is poorly developed in Gazestan. Potassic alteration marked by development of K- as well as biotite is only locally developed in Gazestan. Boron metasomatism occurs as quartz-tourmaline bands and disseminated grains in altered rocks. The scarcity and local nature of sodic (albitic) and calcic-iron (actinolitic) alterations, and the widespread and proximal chlorite alteration suggest that, compared to most other iron deposits of the Bafq district, Gazestan formed at relatively lower temperatures and possibly shallower depths.
