Geology, petrology and geochemical characteristics of alteration zones within the Seridune prospect, Kerman, Iran

The Seridune district consists of an Eocene volcanic andesite succession with a gently northeast dipping, which was intruded by at least two phases of copper bearing granodiorite porphyries. They are subsequently referred to as “granodiorite stock”, and affiliated “granodiorite dikes” (Late Miocene). Furthermore, a late barren dike of intergranular quartz monzonite also intruded into the volcanic andesite. A succession of volcanic dacite lava (Pliocene) overlies the intrusions mainly at the west part of the Seridune district. The volcanic andesite rocks are characterized by plagioclase grains (An85 35) and are classified as low K calc alkaline rocks. The least altered porphyritic granodiorite contains zoned plagioclase (An50 20) and hornblende with quartz, biotite, magnetite and minor ilmenite. These mineral phases are set in an interstitial medium grained quartz and plagioclase groundmass. The porphyritic granodiorite is discriminated as a medium high K calc alkaline suite. The intergranular quartz monzonite consist of hornblende, plagioclase (An50 40), quartz, biotite, and minor magnetite which are crystallized under equilibrium condition. The MREE and HREE patterns are useful indicators to distinguish the mineralized granodiorite porphyry from the barren intergranular quartz monzonite rocks. Geochemically, the Al2O3/(CaO + Na2O + K2O) ratio (0.90 to 0.93) and the Na2O content (> 4.44 wt.%) classify the Seridune granodiorite porphyries into weakly crustal contaminated I type granitoid. The total Al (AlT) content of biotite (2.49 apfu) indicates that the granodiorite pluton was emplaced at approximately 3.9 km below the paleosurface. The early chlorite epidote (propylitic) alteration zone at the Seridune prospect shows a general enrichment in Mg and Ca, which is consistent with the presence of clinochlore, epidote and calcite. The XMg of chlorite decreases from the proximal to distal portion of the chlorite epidote alteration zone, but the Fe values increases outward. The fO2 and fS2 estimated from chlorite compositions range from 10 38 to 10 44 and 10 13 to 10 16 respectively in the chlorite epidote alteration zone. The abundance of epidote veins in distal parts of the propylitic alteration zone coincides with an increase of epidote activity (aCzo). The transitional quartz sericite alteration zone, referred to as “feldspar destructive alteration”, is typically dominated by sericite (XK = 0.86) completely replacing biotite (XMg > 0.60), chlorite (XMg = 0.68) and plagioclase (An50 10). The XK (0.86) of fine grained hydrothermal sericite from the proximal (quartz stockwork) phyllic alteration zone is considerably higher than that from distal portions of phyllic zone (XK = 0.77). The pervasive sericitization and breakdown of plagioclase represent the high activity of K in the hydrothermal fluid through the quartz sericite alteration zone. The presence of quartz veins (“A” and “B”) in the center of the phyllic alteration zone indicates that it overprints the earlier subsurface potassic alteration zone. The common sulphides consist of fine grained pyrite and chalcopyrite, which occur in the “B” quartz vein/veinlets or disseminated in the selvage of quartz sericite alteration zone. These veins are present in the center of phyllic alteration zone (quartz stockwork zone) and disappear outside of the center. The microthermometric data from the fluid inclusions related to quartz veins/veinlets in phyllic alteration zone indicate that the homogenization temperature (Th) and salinity are in the approximate range of ~273°C and 17.9 wt.% NaCl eq respectively. The quartz clay (argillic) alteration is characterized by bleaching of abundant feldspars which is the primary indication of the argillic alteration at the Seridune prospect. The composition of the relict feldspar is An30 10 and the mole fraction of XK in feldspar varies from 0.35 to 0.14. The alteration shows a decrease in the mass and volume ( 1.48± 12.2 % and 1.03± 10.13 % respectively) with respect to the quartz sericite alteration zone. The late quartz alunite pyrophyllite zone is enriched in Al and Si, which reflects the predominance of aluminosilicate minerals, i.e. pyrophyllite, alunite and clay minerals in altered rocks. The sericite and minor K feldspar are mainly replaced by alunite and pyrophyllite, which are unlikely to be formed in equilibrium. The activity of pyrophyllite is about 0.96 through the alteration zone due to the complete destruction of the preexisting minerals. Pyrite occurs as disseminated grains or in the late comb and banded, “D” quartz vein/veinlets of the advanced argillic silicic zone. The microthermometric data of fluid inclusions in comb quartz veins indicate that the Th and salinity are about 246°C and 13.5 wt.% NaCl eq. The fluid density in the late advanced argillic alteration zone is typically lower than that in the transitional phyllic zone, which indicates that the late fluid is more diluted by the meteoric water. The activities of hydrothermal sericite from central quartz sericite, through quartz clay and to late quartz alunite pyrophyllite zones have average aMs values of 0.62, 0.29 and <= 0.007, respectively. Sulphides originally present in the leached capping have been oxidized to limonite, composed mostly of jarosite, goethite, and hematite. The moderate pH (6 8) and Eh (> 0.5 V) solutions control the abundance of other supergene minerals (e.g. malachite and azurite) above the groundwater table. The composition of felsic intrusions, geometry of hydrothermal alteration zones, mineralization styles (porphyry and vein types) and similar geochemical parameter with Sarcheshmeh copper deposit are most important indicators that imply the occurrence of a porphyry copper mineralization at the Seridune prospect.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2007

Author dc:creator

• Barzegar, Hassan

Contributors dc:contributor

• Meyer, Franz Michael

• info:eu-repo/classification/ddc/550
• Seridune
• Alterationszonen
• Geowissenschaften
• Alteration zone

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-124065%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:62499