Browsing by Subject "Pulju Greenstone Belt"

The Pulju Greenstone Belt (PGB), located on the northwesternmost edge of the Central Lapland Greenstone Belt (CLGB) in Finland, bears significant potential for Ni-sulfide deposits. The Paleoproterozoic differentiated komatiites of the Mertavaara Formation host the Hotinvaara Ni-prospect which is the most economically promising mineralization to date within the PGB. Following the completion of ~ 15.52 km addition diamond core drilling, Nordic Nickel Ltd. completed the Mineral Resource Estimate (MRE) for the Hotinvaara Ni-prospect, indicating 418Mt at 0.21% Ni, 0.01% Co, and 53ppm Cu for 862,800t of contained Ni, 40,000t of contained Co and 22,100t of contained Cu. The Hotinvaara mineralization occurs in strongly metamorphosed MgO-rich olivine cumulates as moderately- to weakly-interconnected sulfide disseminations and as larger pentlandite-pyrrhotite blebs. In addition, Ni-sulfides occur locally as massive 10’s of cm to m-scale, sulfide veins containing up to 9.61% Ni, 0.17% Cu, and 0.36% Co. Mineralized offsets are also found within the metasedimentary rocks of the Sietkuoja Formation and mafic to intermediate tuffites of the Vittaselkä Formations; however, these occurrences are mainly pyrrhotite-dominant and do not have economic interest. Chalcopyrite, pyrite, mackinawite, cobaltite-gersdorffite, violarite, and valleriite are present in subordinate amounts (<5%). All mineralization types have been subject to multistage deformation events (D1-D4) at lower-amphibolite facies metamorphic conditions, which led to the development of deformation textures, recrystallization, and annealing of sulfides as well as paragenetic relationships indicating remobilization of sulfides. On average, the sulfide phase contains 12.63 wt.% Ni and 0.59 wt.% Co, 0.54 wt.% Cu, and very low PGE abundances, implying that the sulfide fraction of the Hotinvaara Ni-prospect is Ni-(Co)-enriched and Cu-PGE-depleted. Nickel contents of the sulfide phases are extremely variable (1–36 wt.%) at Hotinvaara, even between closely spaced samples, reflecting the effect of post-mineralization metamorphism and deformation that has resulted in the loss of S. Electron Probe Microanalyser (EPMA) data imply that Ni is moderately partitioned into pyrrhotite (0.01–4.60 wt.%) and pyrite (0.01–0.65%); and Co is strongly partitioned into pentlandite (0.19–5.42 wt.%) and pyrite (0.01–4.01 wt.%), which is reflected in the sulfide mineralogy as Co-bearing pentlandite, Ni-rich pyrrhotite, Ni-Co-rich pyrite, and trace cobaltite-gersdorffite are ubiquitous sulfides at Hotinvaara. LA-ICP-MS results reveal that the recrystallization of pyrrhotite, pentlandite, and pyrite resulted in the loss of some trace elements such as Zn, Mo, Ag, Sn, Sb, Pb, and Tl from the sulfides. In contrast, the elevated concentrations of Ni and Co in the same samples indicate that these elements tend to remain in the lattice of sulfides during metamorphic recrystallization. High As/Se and moderate to low Sb/Se ratios in pentlandite suggest extensive assimilation of black shales into the komatiitic intrusion of the Mertavaara Formation. Even though primary magmatic sulfide textures are not preserved at Hotinvaara, high Se/As and low Co/Sb ratios in pyrite imply that this sulfide phase has a magmatic origin. This most likely indicates that other sulfide phases genetically bonded to pyrite (e.g. pyrrhotite, pentlandite, and chalcopyrite) are also magmatic in origin.