Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The partition coefficients of platinum group elements (PGE) and chalcophile elements Au, Re, Ag, Se, Bi, Te, and Sb, between arsenide and sulfide phases (D (super As/sulf) ) have been estimated by measuring in situ concentrations of these elements using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in coexisting arsenide and sulfide minerals from the Beni Bousera Cr-Ni mineralization (North Morocco). Previous experimental studies and observations on the distribution of PGE in a number of As-rich, Ni-Cu-PGE ore deposits have shown that arsenide minerals may play an important role controlling the distribution of these metals in magmatic sulfide systems. However to date, there is no comprehensive study quantifying the partitioning behavior of these elements when arsenide minerals crystallize either directly from a sulfide melt or from an arsenide melt previously segregated by immiscibility from a sulfide melt. The Beni Bousera mineralization represents an excellent natural laboratory to evaluate these partition coefficients because maucherite (Ni (sub 11) As (sub 8) ) coexists in equilibrium with pyrrhotite, pentlandite, and chalcopyrite in form of globules mostly associated with pyrrhotite, and arsenide and sulfide minerals account for the bulk of the PGE (with the exception of Pt) and chalcophile elements in the samples. The laser ablation analyses reveal that maucherite is strongly enriched in all chalcophile elements, except Se, relative to sulfide minerals. The calculated D (sub PGE) (super As/sulf) are the following: D (sub Ir) (super As/sulf) = 920 D (sub Rh) (super As/sulf) = 620, D (sub Pt) (super As/sulf) = 330, D (sub Pd) (super As/sulf) = 250, D (sub Os) (super As/sulf) = 140, and D (sub Ru) (super As/sulf) = 50. For the rest of elements, the obtained values are the following: D (sub Sb) (super As/sulf) = 890, D (sub Te) (super As/sulf) = 190, D (sub Bi) (super As/sulf) = 50, D (sub Re) (super As/sulf) = 6, D (sub Au) (super As/sulf) = 310, D (sub Ag) (super As/sulf) = 4, and D (sub Se) (super As/sulf) = 0.6. These results clearly highlight the strong affinity of PGE for arsenide phases and the importance of these phases as potential carriers of PGE in Ni-Cu-PGE ore deposits.