Sfaleryt w osadach kredy synklinorium szczecińsko-mogileńskiego

Abstract

SPHALERITE IN THE CRETACEOUS DEPOSITS OF THE SZCZECIN-MOGILNO SYNCLINORIUMSummaryDark-coloured  sphalerite has been ascertained to occur in the Cretaceous  deposits of the Szczecin- Mogilno synclinorium  area. Its presence has been recorded in three bore holes: at Pagórki (Pagórki IG 1) where it occurs in Weald limestones, at Wągrowiec, in strongly arenaceous clay siderites of Hauterivian age, and at Oświno – in the Upper Albian glauconite sandstones, characterized by cellophane cement. The sphalerite  occurring at Pagórki  is thought to be genetically connected with calcite veinlet. At Wągrowiec, it is abundant in siderite-clayey cement, in the form of aggregates of frequently intergrown  grains. Size of the individual grains reaches here up to 2,0 mm.At Oświno, occurrence of sphaleriteis, first of all, genetically connected with calcite veinlets. As a rule, the grains of the sphalerites show idiomorphic forms, their diameter attaining 0,5–0,3 mm in diameter, disseminated in the cellophane cementing material.X-ray powder analyses made after the admixture of NaCl have allowed to calculate unit cell that, for the sphalerite  from Wągrowiec, are 5,410 A ± 0,003, and for that from Oświno – 5,409 A ± 0,003. Index of reflaction for sphalerite  from Oświno, measured on goniometer in sodium light, ammounts to n =2,418 A ± 0,002. The sphalerites from Wągrowiec and Oświno were chemically analyzed, as well. It has been started that after transformation of the results of chemical analyses into mineral composition, and after rejection of insoluble particles, regarded here as mechanical admixtures, the percentage by weight of FeS in  sphalerite  from Wągrowiec amounts to 7,71% and that in sphalerite from Oświno to 3,60%.According to the literature data, sphalerites revealing such iron contents should be far lighter than those here considered, with are dark-brown on colour. On the basis of the iron contents, we shoud accept here that the sphalerite from Oświno has been formed at a temperature amounting to about 130°C, and that from Wągrowiec about 180°C. These temperatures suggest the hydrothermal origin of the sphalerites in study. Considering their genesis, we should take into account that all the bore holes, in which sphalerite has been encountered, are situated within the Szczecin- Mogilno through, at the foot of the southern slope of the Middle Polish anticlinorium. According to W. Pożaryski (1960), in this area the Cretaceous deposits have reached their greatest thickness that amounts to 3000 m.  during the uplifting processes of the Middle Polish anticlinorium, dese deposits firstly underwent great pressure, and then were yielded to stretching forces responsible for considerable fractures. At that period conditions existed for free migration of solutions, causing sedimentation of calcite, to a lesser degree also of sphalerite in fissures. In the first period of uplifting of the anticlinorium, the solutions bearing sphalerite, were probably squeezed out from deeper zones of the earth crust, and it is not necessary to connect these solutions with a concrete deep-seated magmatic source.