Investigation of gold and base metals mineralization and the petrochemical studies of the associated host rocks, Shagari Bala area, Skardu GilgitBaltistan, Pakistan
Keywords:
Gold; Base metals; Petrochemistry; Meta-volcanics; Gilgit-BaltistanAbstract
The Shagari Bala area lies in the Skardu district of Gilgit-Baltistan province. It is located within the Kohistan-Ladakh island arc on the east side of Nanga Parbat Haramosh massif. Deosai volcanics and the meta-volcanics of the Burji-La Formation, mainly exposed in the study area are the focus of this study. The Deosai volcanics are partially to highly altered porphyrictic rocks while the meta-volcanics of the Burji-La Formation are metamorphosed to greenschist facies. The Deosai volcanics also have suldes-bearing mineralized altered zones which exhibit leaching of chalcopyrite and pyrite to malachite, azurite and limonite.
The petrographic studies show that the Deosai volcanics have porphyritic texture and mainly comprised of plagioclase and hornblende phenocrysts. Plagioclase phenocrysts are generally partially altered but the completely altered phenocrysts are also not common. Hornblende phenocrysts are usually replaced by chlorite and epidote. Phenocrysts of plagioclase and hornblende along with alkali feldspar, quartz and ores are embedded in felsophyric groundmass. The feldspar phenocrysts and the groundmass are generally altered to kaolinite, sericite and saussurite. The meta-volcanics of the Burji-La Formation consists of amphibole (mainly tremolite/actinolite with lesser amount of hornblende), plagioclase, epidote, alkali-feldspar, chlorite and ores. Epidote and chlorite are the alteration products of hornblende while kaolinite, sericite and saussurite are the alteration product of feldspar.
The gain and loss in gold, silver and base metals in the hydrothermally altered suldes-bearing mineralized altered zone have been evaluated on the basis of enrichment and depletion factors. Multifold enrichment of Au, Ag and Cu are found in these zones. However, this enrichment is not of economic importance.
The geochemical studies show that the Deosai volcanics are dacite to rhyodacite in composition while the meta-volcanics of Burji-La Formation show basalt to basaltic-andesite in composition. The spider diagrams of both Deosai volcanics and the meta-volcanics of the Burji-La Formation exhibit enrichment of large ion lithophile elements as compared to high eld strength elements while well-dened negative and positive anomalies have been observed for Nb and Sr respectively. The major and trace elements data of Deosai volanics and the meta-volcanics of the Burji-La Formation were evaluated for identifying the paleotectonic environment of their formation. It has been noticed that the studied volcanics are of calcalkaline character which have been originated in the island arc type of setting mainly involving subduction related magmatism.
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