The Penikat layered intrusion belongs to the 2.44 -2.5 Ga mantle plume related magmatism, manifested by numerous large layered intrusions in Finnish Lapland and Kola.The Penikat intrusion comprise of five megacyclic units (MCU I to V (top)) with three major PGE reefs.The Sompujärvi reef (SJ) occurs at the base of the MCU IV, the Ala-Penikka reef (AP) within the MCU IV, and the Paasivaara reef (PV) at the upper-most part of the MCU IV.In-situ Sr-isotope compositions of plagioclase are analysed to constrain the petrogenesis of the Penikat intrusion and its PGE reefs.The results show a mild change in initial Sr isotope compositions at the lower part of the intrusion, upwards from MCU I to MCU IV.The MCU IV records the lowest most Sr(i) values within the Penikat intrusion, yet a transgressive shift towards more radiogenic signature is observed at the transition zone between MCU IV and V.The data indicates that different types of magmas have been involved in the Penikat intrusion, and magma mixing may have played a role in the formation of the PV reef in particular.
Abstract Chromium-zoning patterns in pyroxene from the economically significant Ni-Cu sulfide deposits at Nova-Bollinger (Western Australia) and Kevitsa (Northern Finland) were investigated using XRF mapping, automated mineralogy, and EPMA analyses. At Nova-Bollinger, complex Cr-zoning patterns are found widely throughout the cumulus orthopyroxene and clinopyroxene within the Lower Intrusion, a small chonolith that hosts the vast extent of the sulfide mineralisation. Cumulus pyroxenes with visible sector and abrupt zonation patterns have been found up to 150 m vertically away from the massive sulfide ore. Complex zoning patterns are observed throughout the Kevitsa intrusion, in the form of strong oscillatory zoning in cumulus clinopyroxene and sector zoning in idiomorphic orthopyroxene oikocrysts. Kevitsa pyroxenes show varying degrees of hydration, leading to epitaxial replacement by amphibole. Cr zonation is visible through the early stages of this alteration, with preservation enabled by the presence of Cr-rich epitaxial amphibole; however, the remnant zoning is lost as the amphibole alteration progresses. Results suggest that Cr zonation in pyroxene may be an effective indicator of dynamic recharged conduits and therefore an indicator of favourable conditions for metal enriched magmatic sulfide ore formation. Such indicators have significant vertical extent from the ore body and can survive partial alteration, which makes them a useful tool for prospectivity assessment of drilled intrusions. Furthermore, our data show that there is potential for complexly zoned pyroxene to be used as an ex-situ prospectivity indicator in glacial till.
Kevitsa has been one of Europe's most important nickel mines.To enhance our understanding of the ore-forming and post-magmatic processes that occurred in the Kevitsa intrusion, we determined PGE concentrations of the main sulphide phases from the main ore types using laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS).Although the origin of the Ni-PGE ore remains ambiguous, it is clear that the formation was dominated by magmatic processes and hydrothermal redistribution of metal played an insignificant role.
Low grade sulfide ores are difficult to process due to their composite mineralogy and their fine grained dissemination with gangue minerals. Therefore, fine grinding of such ores becomes essential to liberate valuable minerals. In this research, selective flotation was carried out using two pitched blade turbine impellers with diameters of 6 cm and 7 cm to float copper and nickel. The main focus of this research was to generate optimum hydrodynamic conditions that can effectively separate nickel and copper from gangue minerals. In addition, we investigated the effects of superficial gas velocity, impeller speed, bubble size distribution, and bubble surface area flux on the flotation recovery and rate constant. The results demonstrated that a 7 cm impeller comparatively produced optimum hydrodynamic conditions that improved Cu-Ni recovery and the rate constant. The maximum copper and nickel recoveries in the 7 cm impeller tests were observed at 93.1% and 72.5%, respectively. However, a significant decrease in the flotation rate of nickel was observed, due to entrainment of nickel in copper concentrate and the slime coating of gangue minerals on the nickel particle surfaces.
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