Petrology of Precambrian metagranites and heavy mineral chemistry of the Olounou area within the Cameroon mineral belt (Ntem Complex, South Cameroon): relationships with the Fe-mineralization

The petrology of Achaean biotite- and amphibole-rich metagranites, the geochemistry of Fe-occurrences and heavy mineral concentrations in stream sediments from Olounou (Ntem complex) help to constrain their inter-relationships. These metagranites display granoblastic textures outlined by microcline, biotite, amphibole and oxides. Ilmenite (60 to 80%), zircon (15 to 20%) and rutile (1 to 2%) are the mineral fractions in pan concentrates. Two types of Fe-mineralization as silicified veins crosscut the above rocks: hematite± magnetite quartzites with primary hematite enclosing magnetite relicts contain high average Fe2O3 (69.05 wt %) and TiO2 (0.73wt %); banded magnetite-rich quartzites with magnetite partially replaced by hematite are characterized byFe2O3 (52.15 wt %), TiO2 (0.27 wt %), relatively high W (286 ppm) and Ni (108 ppm). Both types have Zn, Cu, Ga contents below 10 ppm, positive Eu anomalies, HREE enrichment over LREEs and low ∑REE (9.76 to 12.07). Iron and SiO2 were derived from weathering of Archean biotite and amphibole metagranites, deposited in existing Post-Archean intra-cratonic basins under greenschist facies and impacted by sub-marine hydrothermal solutions. These results are genetically comparable to other Precambrian BIFs and underline the iron potential of Olounou. They equally contribute to iron ore exploration in Cameroon and worldwide.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5426547

Shear-Hosted Uranium Deposits: A Review

A group of uranium deposits is described that is hosted within polyphase shear zones. The group is economically significant, collectively containing over 500,000 tonnes of uranium and several examples have been or are being mined. Over a hundred individual deposits are known widely spread over many countries. It is proposed that this group be assigned to a new shear-hosted uranium deposit category. Uranium deposition was superimposed upon intense and extensive feldspathic alteration formed during ductile deformation. This intense alteration has led to the alternative albitite-type or metasomatite-type nomenclature. The evidence is clear that in most cases uranium mineralization postdates regionally extensive feldspar alteration and is associated with a range of alteration assemblages which overprint early albite or K-feldspar dominant alteration. Abundance of hydrothermal zirconium and phosphate minerals is a common characteristic of this group which implies high activity of F and P during mineralisation, but the source of hydrothermal fluids remains uncertain. Also uncertain is the geodynamic setting of uranium mineralisation which is a consequence of absolute mineralisation age being poorly defined. Data from three of the four major districts are suggestive that mineralisation was a consequence of fluid migration along shears during regional compression. This paper reviews key aspects of the group in a mineral systems context, focussing on the four major districts of Kropyvnytskyi (Ukraine), Lagoa Real (Brazil), Mount Isa (Australia) and the Central Mineral Belt (Canada).

Caseyite, a new mineral containing a variant of the flat-Al13 polyoxometalate cation

Caseyite, [(V5+O2)Al10–x(OH)20–2x(H2O)18–2x]2[H2V4+V95+O28][V105+O28]2[(Na,K,Ca)2–y(SO4)2–z⋅(60+8x+y+4z) H2O], where x = 0–2.5, y = 0–2, z = 0–2, is a new mineral (IMA 2019-002) occurring in low-temperature, post-mining, secondary mineral assemblages at the Burro, Packrat, and West Sunday mines in the Uravan Mineral Belt of Colorado, U.S.A. Crystals of caseyite are yellow tapering needles or blades, with a pale yellow streak, vitreous luster, brittle tenacity, curved fracture, no cleavage, Mohs hardness between 2 and 3, and 2.151 g/cm3 calculated density. Caseyite is optically biaxial (+) with α = 1.659(3), β = 1.670(3), γ = 1.720(3) (white light), 2V = 52.6(5)°, has strong r < ν dispersion, optical orientation Z ≈ a (elongation of needles), and no pleochroism. Electron-probe microanalysis provided the empirical formula [(V5+O2)Al8.94(OH)17.88(H2O)15.88]2[H2V4+V95+O28][V105+O28]2[(Na0.82Ca0.35K0.27)Σ1.44 (SO4)1.33⋅70.24H2O] (+0.94 H). Caseyite is monoclinic, P21/n, a = 14.123(8), b = 30.998(15), c = 21.949(11) Å, β = 97.961(8)°, V = 9516(9) Å3, and Z = 2. The crystal structure (R1 = 0.0654 for 9162 Io>2σI reflections) contains both normal [V10O28]6– and doubly protonated mixed-valence [H2V14+V95+O28]5– decavanadate isopolyanions, and a novel vanadoaluminate heteropolycation (“flat-Al10V☐2”), ideally [(V5+O2)Al10(OH)20(H2O)18]11+, closely related to the technologically important flat-Al13 polyoxocation.

Ore mineralogy of the Chisel Lake Zn-Cu-Ag (+Au) VMS deposit in the Flin Flon – Snow Lake Domain, Manitoba, Canada

The Chisel Lake deposit, in the Flin Flon – Snow Lake Mineral Belt in northern Manitoba, is characterized by an ore mineral assemblage dominated by pyrite and sphalerite, with minor chalcopyrite, galena, and pyrrhotite and trace amounts of other Cu-, Fe-, Sb-, Sn-, As-, Ni-, and Ag-bearing sulfides. Silver is hosted in a variety of Ag-bearing sulfides (chalcopyrite and freibergite–argentotennantite series) and its own sulfide (acanthite). The major elements chemical compositions of the ore sulfides define two populations of sphalerite (Fe-rich and Fe-poor), three populations of chalcopyrite (pure, Ag-rich, and Ag- and Sb-rich), and a typical galena, in addition to pyrite and pyrrhotite. Trace elements are dominated by Mn and Cd for sphalerite; Sn, Zn, and Ge for chalcopyrite; Se and Ni for pyrrhotite; and As and Co for pyrite. Formation temperature was best estimated, from the Fe and trace elements (Ga, Ge, Mn, and In) concentrations in sphalerite, at approximately 340 °C, with other methods giving less reliable temperature and pressure estimates.