Copper mineralization in rodingites from Ano Garefi, Aridea area, Northen Greece

Περίληψη

The aim of this B.Sc. thesis was to study the mineral assemblages of the rodingites from Ano Garefi in Aridea area (Northern Greece) and to verify the conditions under which these rocks were formed and in particular to consider the not so common associated copper mineralization in terms of the rodingitization process. The study area is the mountainous terrain above Ano Garefi village which geotectonically belongs to the Almopia subzone of the Axios zone. The Ano Garefi rodingites occur as pods, veins and blocks enclosed in serpentinites and usually adjacent to small or large tectonically included carbonate bodies. Macroscopically, these rodingites have a pale green-brown color while their mineral constituents are medium- to coarse-grained. The identified mineral assemblages consist of calcite + garnet + epidote + clinopyroxene + chlorite ± chromite + chalcopyrite ± pentlandite ± sphalerite. Calcite occurs as local clasts, as veins or even as extended masses enclosing the silicate minerals. Garnets are usually well crystallized and display marked birefringence and anisotropism. A sector zoning and a chemical differentiation from core to rim can be found in most of the garnet crystals. Chemically, they belong to the ugrandite series with andradite as the dominant end-member. The rims of the garnet crystals are usually overgrown by a thin epidote crust. Epidote also forms separate euhedral and prismatic crystals. The clinopyroxenes found within the Ano Garefi rodingites are of diopside-hedenbergite composition. Additionally, wollastonite compositions were found as a result of enrichment in terms of Ca due to the close contact between the rodingites and the carbonate bodies. Chlorite forms small pale green flakes interstitially found to the other minerals and has a pycnochlorite composition. Chromite is a relic mineral of serpentinite protolith and occurs as partly altered to ferritchromite fractured clasts showing evidence of tectonic deformation. The ore
minerals, consisting mainly of chalcopyrite with minor pentlandite and sphalerite can be found as local segregations filling the interstices between the gangue minerals. The sulfide mineral content approximately accounts for about 5% by volume of the rodingite body. Chalcopyrite from Ano Garefi has a typical chemical composition with atomic proportions of Cu and Fe, based on 2 S, in the range of 0.824-1.081(mean 0.944) and 0.827-1.040 (mean 0.931), respectively. Pentlandite is a cobaltian variety, with atomic proportions of Co, Fe and Ni, based on 8 S, in the range between 4.912- 5.961 (mean 5.312), 0.911-1.580 (mean 1.188) and 1.604-2.682 (mean 2.008), respectively. Sphalerite is characterized by relatively low iron contents. Based on 1 S, Zn ranges between 0.860-0.935 with a mean value of 0.896 while Fe ranges between 0.022-0.054 with a mean value of 0.039. Textural features and mineral associations of the copper bearing rodingites in study, denote that their formation can be attributed to a metasomatic process by means of hydrothermal fluids. These fluids were enriched in the necessary chemical elements by the depletion of the surrounding rocks and circulated through tectonically weakened zones. The reaction zone occurs between carbonate bodies and serpentinites. The carbonate bodies are the main source of Ca while serpentinites are the source of Fe and Mg. Dolerites, associated with the serpentinites, are the most likely source for Al and Cu.