Gold deposits associated with the gabbroic rocks at Tirek area, western Hoggar, Algeria: fluid inclusion study
- 128 Downloads
The Tirek gold deposit hosted in the Archean shield is one of the richest sources of mined gold for Algeria. The deposit is controlled by the East Ouzzal shear zone (EOSZ), a transcurrent N–S lithospheric fault. The EOSZ is a late Pan-African dextral-ductile shear zone separating two contrasting Precambrian domains: the Archean In Ouzzal block to the west (Orthogenesis with subordinate metasediments reworked and granulitized during the ca. 2 Ga Eburnean event) and a middle Proterozoic block to the east involved in the ca. 600 Ma Pan-African event. The auriferous quartz veins are mainly oriented in two directions, N–S veins hosted in mylonitic rocks and NE–SW veins hosted in gabbroic or gneissic bands. The NE–SW veins contain the richest ore. Gold ore is found in a system of veins and lenticular quartz veinlets arranged in anastomosing networks. The hydrothermal alteration associated with these veins is characteristically a carbonate-sericite-albite-pyrite assemblage. Gold is the main metal of economic importance; it is disseminated in the quartz as grains or fibers along microcracks and as microscopic grains in the host rocks. Microthermometric results and Raman laser data from fluid inclusions demonstrate that the ore-forming fluids contained H2O-CO2±CH4 and were low salinity. Homogenization temperatures are commonly 250–310 °C. In the Tirek deposit, the role of the shear zone that hosts the mineralization was to drain the hydrothermal fluid. Interactions between the fluid and the mafic host rocks and CO2 also contributed to the formation of the hydrothermal gold deposit at Tirek.
KeywordsTirek gold deposit Shear zone Hoggar Fluid inclusions
The manager and staff of Tirek-Amesmessa Gold Mine are deeply appreciated for their assistance during the field work.
Honest thanks are extended to the staff of the Department of Engineering and Mineral Resources, Kyushu University, Japan. Especially the Associate professor Mr. Kotaro Yonezu, Mr. Hakim Saibi, Dr. Thomas Tindell, and Dr. Jillian Aira Gabo.
The laboratory analysis was financially supported by JASSO scholarship.
- Aissa DE, Marignac C, Kesraoui M, Nedjari S, Boutrika R & Guessoum N (2006) Relations entre les minéralisations aurifères et à métaux rares éocambriennes du Hoggar. In:(ed. PIGC) algiers, UNESCO, 485Google Scholar
- Attoum A (1983) Etude géologique et structurale des mylonites pan-africaines et des minéralisations aurifères associées dans le secteur de Tirek. Hoggar, Algérie In FrenchGoogle Scholar
- Boiron MC, Cathelineau M, Trescases JJ (1989) Conditions of gold-bearing arsenopyrite crystallization in the Vileranges basin, March-Combrailles shear zone, France: a mineralogical and fluid inclusion study. Econ Geol 84(5):1340–1362. https://doi.org/10.2113/gsecongeo.84.5.1340 CrossRefGoogle Scholar
- Bowers TS, Helgeson HC (1983) Calculation of the thermodynamic and geochemical consequences of nonideal mixing in the system H2o-Co2-Nacl on phase-relations in geologic systems—metamorphic equilibria at high-pressures and temperatures. Am Mineral 68:1059–1075Google Scholar
- Caby R (1996) A review of the In Ouzzal granulitic terrane (Tuareg shield, Algeria): its significance within the Pan-African Trans-Saharan belt. Journal of Metamorphic Geology 14 (6):659-666Google Scholar
- Caby R (1987) The Pan-African belt of West Africa from the Sahara desert to the Gulf of Benin. The Anatomy of Mountain Ranges:129–170Google Scholar
- Kouadri M (1983) Etude des minéralisations aurifères du district d’In Ouzzal sur l’exemple de Tirek et Amesmessa(SW du Hoggar, Sahara central algérien): pétrographie, minéralogie, géochimie. (In french)Google Scholar
- Leonardos O, Jost H, Oliveira C (1991) Gold deposits and shear zone relationships in the Precambrian of Brazil. Brazil Gold 91:167–169Google Scholar
- Roberts RG (1987) Ore deposit models# 11. Archean lode gold deposits. Geosci Can, 14Google Scholar
- Semiani A, Marignac C, Aissa DE, Fourcade S, Boiron MC, Joron JL, Peucat JJ & Kienast JR (2004) La métallogénie de l’or liée à l’évolution de la chaîne panfricaine du massif du Hoggar (Sud de l’Algérie): influence des socles anté-panafricains dans le processus de mise en place des minéralisations aurifères. Bulletin du service géologique d’Algérie, n°15,133.(In French)Google Scholar
- Sibson RH, Robert F, Poulsen KH (1988) High-angle reverse faults, fluid-pressure cycling, and mesothermal gold-quartz deposits. Geology 16(6):551–555Google Scholar