Christina Wanhainen

Age, petrology and geochemistry of the porphyritic Aitik intrusion, and its relation to the disseminated Aitik Cu-Au-Ag deposit, northern Sweden

Abstract The Aitik Cu-Au-Ag deposit in northern Sweden is hosted by strongly altered and deformed 1.9 Ga old Svecofennian volcaniclastic rocks. A porphyritic quartz monzodiorite intrusion of subvolcanic origin is situated in the structural footwall to the ore. U–Pb TIMS zircon dating of the quartz monzodiorite yielded an age of 1887±8 Ma, which coincides with the age obtained for the subduction-related Haparanda suite of granitoids in Norrbotten. It is intruded by minor, comagmatic phases, including units of finer grained quartz monzodiorite and diorite. The finer grained intrusive phase, which can be traced into the ore zone of the Aitik deposit, is believed to represent apophyses protruding from the upper part of the quartz monzodiorite. The Aitik intrusion, comprising the quartz monzodiorite and its comagmatic phases, is affected by regional metamorphism, deformation, and hydrothermal alteration. Potassic alteration is most evident, and expressed by the growth of secondary biotite and K-feldspar. The sub-economic Cu-Au-Ag mineralization hosted by the Aitik intrusion mainly consists of chalcopyrite, pyrite, and magnetite of dominantly magmatic-hydrothermal origin, and is present in four forms: disseminated, as veinlets, in quartz-feldspar veins, and in biotite-amphibole veins. This mineralization extends in economic grades into the adjacent volcaniclastic rocks in the roof of the intrusion. The Aitik intrusion is similar in many respects to porphyry copper generating intrusions regarding tectonic setting, petrography and chemical composition. The intrusion-hosted sub-economic mineralization might form part of a porphyry system with its major part represented by the main mineralization in the overlying volcaniclastic rocks.

Lithology and mineralisation types of the Rockliden Zn–Cu massive sulphide deposit, north-central Sweden : Implications for ore processing

Abstract The Rockliden Zn–Cu volcanic-hosted massive sulphide deposit is located approximately 150 km south of the Skellefte ore district, north-central Sweden. Most of the mineralisation is found at the altered stratigraphic top of the felsic volcanic rocks, which are intercalated in the metamorphosed siliciclastic sedimentary rocks of the Bothnian Basin. Mafic dykes cross-cut all lithological units, including the massive sulphides, at the Rockliden deposit. The relatively high Sb grade of some parts of the mineralisation results in challenges in handling of the Cu–Pb concentrate in the smelting process. The aim of this study is to characterise different host rock units and ore types by their main mineralogy, as well as by their trace mineralogy with focus on the Sb-bearing minerals. Ore types are distinguished largely on the basis of their main base-metal bearing sulphide minerals, which are chalcopyrite and sphalerite. Several Sb-bearing minerals are documented and differences in the trace mineralogy between rock and ore types are highlighted. Based on the qualitative ore characterisation, rock- and ore-intrinsic parameters, such as the pyrite, pyrrhotite and magnetite content of the massive sulphides, the trace mineralogy and its association with base-metal sulphide minerals, are outlined and discussed in terms of relevance to the ore processing.

Gold mineralogy at the Aitik Cu–Au–Ag deposit, Gällivare area, northern Sweden

The low-grade Aitik Cu–Au–Ag deposit is a deformed and metamorphosed porphyry-type deposit, and as such it belongs to the group of ores that require detailed mineralogical investigations of precious metal occurrences to assist in determining the recovery processes. The character of gold in the Aitik deposit varies substantially. Gold alloys display highly variable Au/(Au+Ag) ratios, and Hg is commonly a constituent. A change from dominantly sulphide-associated to groundmass-associated gold as mining progresses towards depth is accompanied by a change in the chemical composition of gold. Towards depth, the gold content in electrum and amalgam decreases (from c. 66 to 22% in electrum and c. 23 to 4% in amalgam), and the amount of native gold grains increases. The most common mineral assemblage associated with gold at deep levels (600 m and below) is K-feldspar, biotite, plagioclase, quartz, chalcopyrite and pyrite. This study demonstrates that magmatic–hydrothermal and metamorphic processes responsible for the diversity in copper mineralisation styles within the Aitik ore body probably have also played a role in the variable character of gold observed at Aitik today.

Particle-based Sb distribution model for Cu–Pb flotation as part of geometallurgical modelling at the polymetallic Rockliden deposit, north-central Sweden

The polymetallic Cu–Zn ore of the Rockliden massive sulphide deposit in the Skellefte District in north-central Sweden contains a number of deleterious elements in relevant concentrations. Of particular concern is the amount of antimony (Sb) reporting to the Cu–Pb concentrate. The aim of this study was to compare different model options to simulate the distribution of Sb minerals in a laboratory flotation test based on different degrees of details in the mineralogical information of the flotation feed. Experimental data obtained from four composites were used for the modelling and simulation. The following different simulation levels were run (sorted from least to highest level of detail of their mineralogical information): chemical assays, unsized bulk mineralogy, sized bulk mineralogy and particle information. It was shown that recoveries simulated based on bulk mineralogy are mostly within the error margin acceptable in the exploration stage of the Rockliden deposit. Unexpected high deviation in the simulation using particle information from the original recovery has been partly attributed to the fact that recovery of non-liberated particles cannot be modelled appropriately in the present version of the modelling and simulation software. It is expected that the implementation of full particle information in simulation will improve the Sb distribution model for the mineralogically complex Rockliden deposit.

Timing of plutonism in the Gällivare area: implications for Proterozoic crustal development in the northern Norrbotten ore district, Sweden

Zircon ion probe (secondary-ion mass spectrometry or SIMS) data from a set of intrusive rocks emplaced in the vicinity of major ore bodies, as well as from large igneous intrusions in the Gallivare ...