Ultramafites and associated mineralisation Research Papers (original) (raw)

SULFUR SPRINGS IN THE “GRUPPI DI VOLTRI” OPHIOLITE COMPLEX (ITALY) The Voltri Group is an Alpine-type ophiolite complex, which have been affected by the Alpine orogenesis and the consequent metamorphism, that completely canceled the... more

SULFUR SPRINGS IN THE “GRUPPI DI VOLTRI” OPHIOLITE COMPLEX (ITALY)

The Voltri Group is an Alpine-type ophiolite complex, which have been affected by the Alpine orogenesis and the consequent metamorphism, that completely canceled the stratigraphic relationships and gave rise to important green schist facies modifications which often make it difficult to recognize the original nature of the rocks. The most important forming lithotypes are: lherzolites, serpentintinites, metagabbros, prasinites, amphibolites, quartzites, shales: acid crystalline schists are present along the western margin.

Metallic oxides and sulphides are scattered in all lithotypes and locally form discrete massive bodies, such as concentrations of pyrite and chalcopyrite, with other sulphides and sulphosals, in prasinitic rocks and in contact between these and calcescists. However, the most interesting mineralizations are the hydrothermal quartz veins in alterated serpentinites, that form small deposits know in ancient Italian literature as “ydrothermalites”, to day better know as “listwaenites”, or “listvenite” and similar, derived from Russian word. These are stock-work type deposits, mainly composed by quartz and Ca-Mg carbonates with gold, pyrite, chalcopyrite, galena, sphalerite, tetrahedrite, pyrrhotite, and nickel sulphides, cementing crushed breccias near the contact between ultramafics and metabasites, or cutting serpentinites near the above contact.

The presence of a few sulfur springs was known, many others have been identified by the author, and have been analyzed in order to study the relationship with the mineralizations genesis. In particular, the H2S content was analyzed at the source, with the innovative method of GOLTELMAN (1974), in the laboratory the contents of the main elements were then analyzed. All such springs show very similar chemistry; they are medio-mineral type, and can be comprised in a family of sulfur-alkaline springs on the basis of their dissolved substances. Some hydrogeological and geochemical conjectures on the origin of the springs, with particular regard to the H2S, are proposed. The formation of this one is not attributed to biogenic processes, but to chemical reactions promoted by the abundance of metalliferous sulfides.

Another sulfur spring, flowing out from cenozoic sediments very close to the Voltri Group, shows different chemistry and can be comprised in a family of sulfate-alkaline earth springs.