Ferenc Mádai

Klajite from Recsk (Hungary), the first Mn-Cu arsenate mineral

Klajite (IMA no. 2010-004) was found in ore samples from the Lahoca Hill, Recsk, Matra Mountains (northern Hungary). It belongs to the Lahoca epithermal high-sulphidation Cu-Au-As ore deposit, a classical occurrence of enargite. The primary ore consists of enargite, luzonite, pyrite, tennantite, chalcopyrite, galena, and sphalerite. Klajite occurs in the cavities of enargite and quartz, in close association with other secondary minerals: gypsum, jarosite, and an unknown Ca-Cu arsenate. Klajite is a secondary mineral formed by the decomposition of enargite. It forms irregular or sheaf-like aggregates, up to 0.5 mm in diameter, made up of lath-like to thin tabular crystals, typically 0.05–0.2 mm in length. The mineral is translucent, greenish yellow to yellowish green in colour with white streak and vitreous lustre. Its Mohs hardness is about 2–3, the calculated density is 3.213 g/cm 3 . Klajite has a perfect cleavage parallel to {010}, and is extremely brittle; the fracture is uneven. Optically it is biaxial negative or positive with α = 1.595(30), β = n.d. and γ= 1.665(20). It is weakly pleochroic, from colourless to pale green. The chemical composition obtained after correction of electron-microprobe analysis is: MnO 5.67, CuO 32.03, CaO 0.41, As 2 O 5 44.40, H 2 O (calc.) 17.49, total 100.00 wt%. The empirical formula is (Mn 0.82 Cu 0.10 Ca 0.08) ∑ = 1.00 Cu 4.05 As 3.98 O 14 (OH) 2 · 9H 2 O, and the simplified formula is MnCu 4 (AsO 4 ) 2 (AsO 3 OH) 2 · 9H 2 O. The strongest seven lines in the X-ray powder diffraction pattern are [ d hkl in A( I obs %, hkl )] 10.39 (100, 001), 2.916 (64, 202), 2.708 (29, 13), 3.616 (28, 021), 3.050 (28, 022 and 211), 3.956 (27, 020) and 3.110 (24, 122). According to X-ray powder diffraction, klajite is structurally analogous to lindackerite-group minerals; it is triclinic, space group P 1, a = 6.441(3), b = 7.983(4), c = 10.562(3) A, α = 85.28(4)°, β = 80.63(5)°, γ = 84.80(4)°, V = 532.4(3) A 3 , Z = 1. Klajite is named after Sandor Klaj (bom. 1948), a Hungarian mineral collector.

Effect of Bauxite Microstructure on Beneficiation and Processing

The microstructure of bauxite determines to a significant extent the opportunities for its beneficiation and optimum processing downstream. Adequate fine grinding commensurate with its microstructure may result in proper mineral liberation and grain size distribution required for effective ore dressing (i.e. H/M or magnetic separation) and digestion respectively. Particle size distribution, mean diameter and amount of ooidal grains as well as degree of dissemination of the impurities in polished sections of raw bauxite, ground bauxite and red mud samples were determined by means of scanning electron-microscope, electron probe micro-analyser and digital image analysis. The results of beneficiation tests (effective removal of liberated limestone but insufficient reduction of finely disseminated reactive silica) and the required digestion parameters of the mainly oolitic Greek diasporic and the Hungarian boehmitic (partly dolomitic) bauxite are discussed. Based on the microstructure, the effectiveness of beneficiation, the degree of grinding (required particle size) and also the necessary digestion parameters of any bauxite can be adequately predicted.