Copper-silver mineralization at Sam Goosly occurs as a conformable lens within pyroclastic dacites of probable late early Cretaceous age. Most mineralization is contemporaneous with development of aluminous alteration minerals. Distribution zones of scorzalite, andalusite, and an innermost corundum zone, are concentric and broadly outline the mineralized zone. Southwards, along strike, the andalusite zone becomes an andalusite-pyrophyllite zone in which mineralization post-dates aluminous alteration. Regional metamorphlsm has overprinted a propylitic, or greenschist, assemblage on aluminous alteration. Country rocks and mineralization are intruded by two stocks: a 59 ± 3 m.y. quartz monzonite to the west of the ore zone, and a 51 ± 3 m.y. gabbro-monzonite stock to the east. Contact metamorphlsm associated with the gabbro-monzonite has produced a narrow, discontinuous zone of biotite hornfels and recrystallized metallic minerals in the ore zone. Alteration mineral assemblages and sulphide exsolution textures imply temperatures between 350°C and 625°C in the main ore zone. The assemblage andalusite-pyrophyllite-quartz indicates alteration temperatures of about 350°C in the andalusite-pyrophyllite zone. Chemical analysis of the altered volcanic host rocks suggests significant loss of soda and lime, and residual concentration of silica and alumina. These chemical changes probably result from exchange of Na⁺ and Ca⁺⁺ for H⁺ from a hydrothermal fluid, resulting in formation of aluminous minerals and quartz. The value of log mK+/mH+ of the fluid phase is deduced to be between 1 and 2. By analogy with other occurrences, this process probably takes place in a high-temperature solfataric, or geothermal environment. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Science. / Microfiche copy available in Archives and Science. / Bibliography: leaves 111-114. / Ph.D.

Abstract At least 30 gold deposits verified by means of one or more notable diamond drill hole results have been discovered in Central Lapland in the last 20 years, and these can be divided spatially into groups, between which the metal composition varies. The deposits contain varying amounts of sulphides and sulpharsenides as well as gold. Pyrite is the most common sulphide mineral in the gold deposits associated with volcanic rocks, and usually pyrrhotite in those associated with sedimentary rocks. The principal sulphide minerals in those connected with banded iron formations are pyrite and arsenopyrite. A separate group of formations consists of the palaeoplacer gold deposits associated with the molasse-like quartzites and conglomerates of Central Lapland. The iron oxide-copper-gold deposits of Central Lapland, which are a significant potential source of copper and gold, are mostly associated with skarn rocks at the eastern contact of the acidic intrusive rocks of Western Lapland and with skarn rocks occurring as interlayers in metavolcanic and metasedimentary rocks. The gold deposits that have led to actual mining activities in Central Lapland are Saattopora in Kittilä and Pahtavaara in Sodankylä. Apart from the Laurinoja iron oxide-copper-gold ore body in Kolari, copper concentrate has been produced from the Saattopora gold ore deposit and the Pahtavuoma copper ore deposit. Only one gold ore in Central Lapland is being actively exploited at present, that of the Pahtavaara mine, which was worked in 1995–2000 and reopened in 2003. The best starting point for successful gold ore exploration in Central Lapland can be achieved through a thorough knowledge of the deformation zones and their structures and alteration processes and the application of geochemical methods. Magnetic surveys can be of help in identifying and locating deformation zones of interest for exploration purposes and the majority of the associated shear zones and faults. Ore-critical zones usually feature graphite-bearing schists and iron sulphide-bearing sequences that can be traced by electrical methods and used as marker zones to verify the results of geological mapping. Geological, geophysical and geochemical techniques have been used in great diversity, and in particular till geochemistry and bedrock drilling have been methods by which the gold and copper deposits in Central Lapland have been discovered. A total of 7.6 million tonnes of gold and copper ores, including the Laurinoja iron oxide-copper-gold ore, were extracted in Central Lapland over the period 1982–2000. The resulting production of gold during this period was 10 800 kg, together with 21 000 tonnes of copper in concentrates and 4500 kg of silver. The gold and copper ores have been concentrated by gravity separation and/or flotation, since the ores so far taken into production has been of the free milling type. However, a substantial proportion of the deposits in the area contain copper, nickel, cobalt and arsenic as well, in the form of sulphides or sulpharsenides, so that the achievement of commercially saleable products calls for the use of different leaching processes. Deposits have also been found in Central Lapland that have consisted partly or entirely of refractory gold ore in which gold is lying in the crystal lattice of pyrite and/or arsenopyrite, the processing of which by the above-mentioned methods is not economic, as it requires pre-treatment by bio-oxidation or pressure oxidation in order to convert the gold to a cyanide-soluble form.

Call number: LD2668 .T4 1964 H67 / Master of Science

Call number: LD2668 .T4 1965 B87 / Master of Science

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