Metamorphism of Ladakh Island Arc terrain in the Himalayan region: implications from sulfide geochemistry and petrography

• Published in: Arabian journal of geosciences 2023, Vol.16 (10), Article 565
• Main Authors: Farhan, Muhammad, Arif, Mohammad, Ye, Ying, Li, Chun-Feng, Chen, Xuegang, Wu, Tao, Ullah, Zaheen, Turab, Syed Ali, Zafar, Tehseen, Hussain, Zahid, Sadiq, Izhar, Ali, Mubasir
• Format: Article
• Language: English
• Subjects: Amphibolite facies; Amphibolites; Arc deposition; Chalcopyrite; Crystallization; Deformation; Ductility; Earth and Environmental Science; Earth science; Earth Sciences; Fluids; Geochemistry; Igneous intrusions; Inclusions; Island arcs; Lava; Magma; Metamorphism; Metamorphism (geology); Mineral deposits; Minerals; Ores; Original Paper; Petrography; Petrology; Pyrite; Pyrrhotite; Sulfides; Sulphides; Volcanic rocks
• ISSN: 1866-7511; 1866-7538
• DOI: 10.1007/s12517-023-11678-6

The Juji Nala massive sulfide deposit, hosted in the Chota Pani meta-volcanic rocks of the Kohistan-Ladakh Arc, northern Pakistan, has experienced textural and compositional changes due to metamorphism. This study integrates detailed petrographic and mineral chemical investigations to understand the formation of the original deposit and its subsequent modification due to metamorphism and deformation. The study reveals three distinct types of pyrites: a fine-grained disseminated type (Py1), an anhedral type with cataclastic texture and abundant inclusions of other minerals (Py2a), and an anhedral to euhedral type with scarce micro-inclusions (Py2b). The chalcopyrite is fine to medium-grained and forms intergrowth textures with pyrrhotite, Py2a, and Py2b. Marcasite-pyrite aggregates have replaced pyrrhotite and pyrite, whereas chalcopyrite has remained unaffected. Py1 shows a high Co/Ni ratio (> 1) and low Ni content (avg = 76 ppm), suggesting its crystallization from felsic magma-derived ore-forming fluids at temperatures between 366 and 397 °C. The Juji Nala ores have undergone at least four distinct phases of metamorphism, including the cataclastic Py2a formed under greenschist metamorphism, contact metamorphism (upper greenschist to lower amphibolite facies) due to igneous intrusion, thermal annealing, and late-stage cataclasis and retrograde metamorphism during exhumation. In contrast to pyrite, pyrrhotite and chalcopyrite display ductility, and this explains why the pre-metamorphic features of these two minerals were obliterated during metamorphism. This study provides insights into the formation and modification of the Juji Nala deposit, highlighting the importance of considering metamorphic changes in mineral deposits.