ABSTRACT:Parafiniuk, J., Siuda, R. and Borkowski, A. 2016. Sulphate and arsenate minerals as environmental indicators in the weathering zones of selected ore deposits, Western Sudetes, Poland. Acta Geologica Polonica, 66 (3), 493-508. Warszawa.The results of a complex investigation of the sulphate and arsenate assemblages forming in the weathering zone of selected ore deposits in the Sudetes are presented. The development of the weathering zone has been characterised in the polymetallic ore deposits at Miedzianka-Ciechanowice and Radzimowice, and the pyrite deposit at Wieściszowice, which differ in the chemical compositions of the ore and barren minerals and the hydrological conditions. Secondary sulphate and arsenate mineral assemblages vary significantly among the ore deposits under study. Their crystallization is discussed, taking into consideration the stability of particular minerals and the paths of their transformation. It is shown that these minerals have great potential as indicators of weathering processes. A significant role for microorganisms in the formation of the weathering zone of the ore deposits under study is also proven.

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As so ci ate ed i tor: Stanis³aw Wo³kowicz Sec ond ary ar senic min er als (SAM) formed re cently in aban doned adits of the for mer Au-As mine at Z³oty Stok (SW Po land) con sti tute two as sem blages. The first con sists of two types of scorodite, pitticite, kaòkite, hörnesite, picropharmacolite and mi nor amounts of jarosite and gyp sum. For ma tion of the Fe ar se nates took place un der acidic con di tions (pH ~3-4) as a result of löllingite, ar seno py rite and py rite ox i da tion. Hörnesite and picropharmacolite crys tal lized as prod ucts of in ter ac tions be tween acidic ar senic-rich pore so lu tions with Mg-Ca car bon ates from rocks that sur round the ore min er ali sa tion. The in terac tion of car bon ates with acid pore so lu tions caused a rapid in crease in pH that reached neu tral or weakly al ka line val ues. The chem i cal com po si tions of hörnesite and picropharmacolite cor re spond well to their ideal com po si tions: (Mg 3.17 Ca 0.07) S3.24 (AsO 4) 1.90 × 8H 2 O and Ca 4.31 Mg 0.92 (HAsO 4) 1.91 [(AsO 4) 1.99 (SO 4) 0.01 ] S2.00 × 11H 2 O, re spec tively. The sec ond assem blage of SAM com prises ex clu sively the Mg-en riched erythrite [(Co 1.66 Mg 1.03 Ni 0.28 Ca 0.05 Zn 0.02) S3.03 (AsO 4) 1.99 × 8H 2 O)]anna ber gite [(Ni 1.48 Mg 0.94 Co 0.66 Ca 0.12 Fe 0.01 Zn 0.01) S3.20 (AsO 4) 1.92 × 8H 2 O] se ries. These min er als crys tal lized from slightly acidic (pH ~5-6) to neu tral me dia. Dis so lu tion of SAM and other sec ond ary phases (e.g., schwertmannite) causes the release of ar se nate and sul phate ions into mine wa ters. These ions can be re duced un der an aer o bic con di tions by dif fer ent strains of bac te ria. The prod uct of this pro cess is orpiment.

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