Formation and age of sphalerite mineralization in carbonate rocks of Bajocian age in the Swiss Jura Mountains: evidence of Mesozoic hydrothermal activity

Abstract

A combination of petrographic and geochemi- cal techniques was applied to better constrain the origin and evolution of the fluid systems responsible for the for- mation of disseminated, Cd-rich (up to 0.6 wt%), sphal- erite (ZnS) mineralization in the northeastern part of the Jura Mountains, Switzerland. The Rb–Sr ages of sphalerite samples indicate that a main phase of sphalerite formation occurred near the boundary between the late Middle and early late Jurassic, at around 162 Ma. The negative δ34S values (−22.3 to −5.3 ‰) suggest that biogenic sulfide sul- fur was involved in ZnS precipitation. The strontium iso- tope composition is more radiogenic than that of contempo- raneous seawater, reflecting the interaction of mineralizing fluids with silicate rocks. lead isotope signatures are very uniform (206Pb/204Pb = 18.63–18.67, 207Pb/204Pb = 15.63– 15.64, 208Pb/204Pb = 38.51–38.63), indicating an iso- topically well-homogenized fluid system. The basement rocks underlying the Jurassic strata are considered to be the main source of metals for the sphalerite mineraliza- tion. The migration of deep-sourced hydrothermal saline metal-bearing fluids into the Bajocian host carbonates containing sedimentary reduced sulfur resulted in the pre- cipitation of sulfides. The period of sphalerite formation near the Middle–late Jurassic boundary is characterized by enhanced tectonic and hydrothermal activity in Europe, related to the opening of the Central atlantic and tectonic/ thermal subsidence during spreading of the alpine Tethys. Our study provides evidence that the Bajocian carbonate rocks in the Jura Mountains area were affected by the cir- culation of deep-sourced metal-bearing hydrothermal fluids in response to these continent-wide tectonothermal events. The presence of sphalerite mineralization and associated geochemical anomalies in Zn and Cd contents in carbonate rocks may also be used to trace basement features

Elucidating the formation of terra fuscas using Sr–Nd–Pb isotopes and rare earth elements

“…suggest that these interstitial waters caused not only enrichment in REE including Ce but also in other redox-sensitive elements. Alternatively these enrichments might be related to, hydrothermal activities in the course of the opening of the Atlantic Ocean during the late Jurassic and later on, which caused mineralizations including enrichments in Cd, Zn and other redox-sensitive elements in Bajocian carbonates (Efimenko et al, 2014).…”

“…Only a few recent studies focused on the origin of Cd and other trace metal enrichments using the chemical and isotopic characteristics of the Bajocian and Oxfordian limestones (Efimenko et al, 2014;Quezada-Hinojosa et al, 2015). Efimenko et al (2014) suggest that hydrothermal activities could have caused the anomalic trace metal enrichments in those carbonate rocks. However, neither soil, nor saprolite formation and evolution of these carbonate derived systems have to our knowledge been geochemically and isotopically elucidated.…”

Cu and Pb–Zn–Ba deposits in the Great Duchy of Luxembourg: role of brines penetrating the basement and place in the post-Variscan tectonic history of Western Europe

“…Finally, although of little economic importance, the Luxembourg mineral district appears as a missing link between the mineralisation of the Ardennes-Rhenish massifs, on the one hand, and the Upper Rhine graben districts of the Vosges and the Black Forest, on the other. Peng et al 2003;Shu et al 2009;Rongemaille et al 2011) and with the results of experimental (Ohr et al 1994) and natural (Tricca et al 1999) Brockamp et al (2003Brockamp et al ( , 2011Brockamp et al ( , 2015; Cathelineau et al (2004Cathelineau et al ( , 2012; Clauer et al (1996Clauer et al ( , 2008; Efimenko et al (2014); Gigoux et al (2000); Grandia et al (2000); Hagedorn et al (1993); Heijlen et al (2003); Henry bet al (2001);Jowet et al;; Kechra et al (2003); Mertz et al (1991) Schneider et al (1999Schneider et al ( , 2003; Schott and Peres (1987a, b)Symons et al (2009Thiry et al (2006);Timar-Geng et al (2004and Yans (2003).…”

Pb-Isotopic Study of Galena by LA-Q-ICP-MS: Testing a New Methodology with Applications to Base-Metal Sulphide Deposits

“…The initial Pb isotope composition of an ore fluid is best determined from Pb-rich minerals genetically associated with the mineralizing event, e.g., galena (initial U/Pb = 0) [6][7][8][9][10][11] as well as pyrite [4,5,[12][13][14][15][16][17], sphalerite [18], chalcopyrite, and pyrrhotite [19]. In contrast to conventional whole-rock Pb isotope determination of sulphides, which suffers from laborious sample preparation procedures as well as mixing of sulphide phases of potentially disparate petrogenesis, micro-analytical techniques offer the advantage of better textural and intragranular control on the selection of target material.…”