Boccheggiano mines, Montieri, Grosseto Province, Tuscany, Italyi

Regional Level Types
Boccheggiano mines	Group of Mines
Montieri	Commune
Grosseto Province	Province
Tuscany	Region
Italy	- not defined -

Boccheggiano is a village in Tuscany, central Italy, administratively a frazione of the comune of Montieri, province of Grosseto, in the area of Colline Metallifere.

Boccheggiano is about 48 km from Grosseto and 8 km from Montieri, and it is situated along the Provincial Road which links Massa Marittima with Monticiano. It was an important mining village.

The object of exploitation has been the so-called "Boccheggiano lode", a quartz vein with chalcopyrite, pyrite, and other sulfides, sizing over 2 km in length and ranging from 1 to 25 meters in thickness. The main works for copper exploitation date back to 1889-1914, while pyrite was mined from the first decade of the 20th century to 1994.

Boccheggiano is one of the most important historical Italian localities for fluorescent minerals, which yielded literally tons of the so-called “strontian aragonite” or “aragostrontianite” (that is, in most cases, calcite with a very special red fluorescence under LW-UV).

Aragonite, as a metastable polymorph of CaCO3, is normally transformed into calcite, so it is relatively rare in nature. However, the two polymorphs do coexist at Boccheggiano (as proved by means of optical microscope analyses coupled with Raman microspectrography).

Studies on the Boccheggiano carbonate minerals are in progress. According to the available preliminary information (Dallegno et al., 2015), Boccheggiano aragonites are actually Sr-rich, but more important than the Sr content is their content of other chemical elements in specific associations, combined with corresponding variations in morphology (crystal habit), color in non-excited conditions (under natural white light), and in luminescence behavior.

From all these features, it is possible to divide them into three different types. Each type is representative of precise and specific conditions in mineral-forming processes within the multi-stage hydrothermal evolution which deposited both the ore and the gangue minerals, hence the three types are a clear example of typomorphism of carbonate minerals.

In particular, the "type III aragonite" shows both a specific photoluminescence response excited by SW-265 nm UV (carmine-red) and spectrographic features (a broadband red luminescence with a minimum emission also in the blue and green band), due to a specific geochemical pattern which renders it as probably unique in the world. It is an azure colored high-Mg aragonite, normally metastable but preserved in geodes within dolostone levels in the lower part of the Tuscan sedimentary succession, which remained as micro-environments like a closed chemical system during the multi-stage evolution of hydrothermal processes.

Due to the uniqueness of this mineral phase, Dallegno et al. (2015) propose for it the denomination "Boccheggiano-type aragonite" and the locality has to be considered as its "type locality".

The genesis of this aragonite is a key to explain the specific enrichment processes in a precise location of the Boccheggiano extensional fault, which yielded the typical association (as trace elements) of Li, Mo, Sn, Zr, Al, V, Fe and LREEs (above all, Ce, Pr, and La), but also Na, Ba, Mg, and Mn, accompanied by a not negligible content of Sr.

Such association is clearly related to the overall geochemical ‘signature’ of granitoid petrofacies grouped in the Tuscan Magmatic Province (regarding the deep hydrothermal fluids) with probable mixing processes, partial dilution and exchange with shallower hydrothermal fluids crossing the sulphate-carbonate rocks of the Tuscan sedimentary succession (see also http://forum.amiminerals.it/viewtopic.php?t=12039).

Other Databases

Wikipedia:	https://it.wikipedia.org/wiki/Boccheggiano
Wikidata ID:	Q2402810

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References