Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
The Liikavaara Cu-(W) deposit is a small-scale biotite schist-hosted deposit in the Gällivare area of northern Sweden. It is located four km east of the Aitik Cu-(Au) deposit, a renowned world-class porphyry-type deposit with IOCG overprint. Boliden AB, owner and producer of the Aitik mine, also holds exploration permits for the Liikavaara deposit. While Aitik is well-studied, less work has been done on Liikavaara. The last comprehensive study was carried out by Zweifel in 1976. He shows that, despite the proximity to Aitik, Liikavaara differs in e.g. a comparable lower Au/Cu ratio, weak enrichment in Zn, Pb, As, Bi, W, Mo and Sn, and significant occurrence of scheelite. However, data is still insufficient to satisfyingly explain origin and genesis of the deposit. Pursuance of this knowledge is desirable, as advancement in technology now allows a profitable production of Liikavaara. This study aims to describe vein- and mineralisation paragenesis at Liikavaara to gain a better understanding for the origin of the deposit. This is achieved by polarised- and reflected light microscopy and SEM analysis of 20 thin sections from three drill cores through hanging wall, ore zone, and footwall of the deposit. Additionally, a granodiorite intrusion in proximity of the deposit is dated by U/Pb analysis of zircons using multi-collector ICP-MS.The data shows three major types of veins: large aplitic dikes containing quartz-tourmaline veins, various types of quartz-(calcite)-(tourmaline) veins, and calcite veins and veinlets. Veining is abundant and occurs in the host- as well as the wall rock. Ore mineralisation is largely confined to these veins, especially quartz-tourmaline veins in aplite, and quartz-(calcite)-(tourmaline) veins. Ore minerals occur disseminated and in accumulations often associated with calcite and tourmaline. Grain sizes range from fine (<10 µm) to large (>1 mm). Major ore minerals are chalcopyrite, pyrite, and pyrrhotite. Minor ore minerals, though locally enriched, are sphalerite, galena, scheelite, marcasite, and magnetite. Alteration is present throughout the deposit but varies in intensity. Common alteration minerals are biotite, sericite, chlorite, calcite, epidote, tourmaline, and muscovite. Biotite is dominating and it is foliated.Regarding the timing of vein mineralisation, aplites were early, followed by quartz-(calcite)-(tourmaline) veins and late calcite veins and veinlets. For ore mineralisation a paragenetic sequence of magnetite, pyrite, pyrrhotite, chalcopyrite, marcasite, galena, sphalerite, younger pyrite, and scheelite is postulated. Alteration is marked by early biotite and muscovite, followed by sericite, epidote, calcite, and tourmaline, and late chlorite.Based on the results of this study a model for the genesis of the Liikavaara deposit is presented. It formed by overlapping of two porphyry systems with input of material from proximal carbonates. The deposit first developed as a porphyry deposit due to a proximal and small-scale granodiorite intrusion. It then was affected by the quartz monzodiorite intrusion responsible for the Aitik deposit. The distance to this intrusion resulted in the development as a distal porphyry deposit. Late hydrothermal fluids introduced calcite, tourmaline, and scheelite from carbonates in the close surroundings.The granodiorite intrusion suggested to be responsible for the initial formation of the deposit has been dated in this study. 68 zircons are dated for a total of 80 measurements. The zircons show very high lead contents compared to standards, at least partly due to inclusions of common lead. The U/Pb analysis results in an approximate age of 1.87 Ga which is similar to the Aitik quartz monzodiorite. To further refine the findings of this study, a more detailed study of the alteration paragenesis of the deposit, a study of the mineralogy and chemical composition of the carbonates in the area, and dating of the aplitic dikes are recommended, as well as structural geological and geophysical surveys.
2016. , 111 p.
Technology, Liikavaara, Northern Sweden, Mineralogy, Geochronology, Scheelite, Copper, Porphyry