"The mineralisation style at Veovaca and Rupice is considered by the Geological Institute in Bosnia to be of sedimentary exhalative (SedEx) origin. However, there is limited information to confirm the presence of finely laminated or bedded sulphide ore that characterise this deposit type (Figure 13). Furthermore, the presence of chalcopyrite and gold mineralisation particularly at Rupice and extensive breccia-hosted mineralisation precludes the SedEx model (Figure 14).
A possible model for the Vares mineral field is a hybrid SedEx-volcanogenic massive sulphide (VMS) deposit style known as Besshi-style VMS, whereby hydrothermal fluids of volcanic affinity deposit associated metals into the sedimentary environment in a similar way to SedEx mineralisation but driven by volcanic processes rather than sedimentary processes and on a smaller scale. In the Besshi model, there are many common features including syn-deposition of mineralisation and presence of barite; however, the mineralogy and breccia textures are substantially different to those in a SedEx model (Andrews, 2014)."
I wonder if they haven't ruled out the SEDEX option too early?
SEDEX deposits are rarer with only about 125 notable SEDEX deposits in the world. Compare that with the 1,090 VMS deposits on my GoogleEarth animation.
SEDEX deposits are bigger on average than VMS deposits with sizes ranging between about 1Mt and 400Mt with a mean size of 20Mt.
VMS deposits are smaller ranging from about 0.1Mt to about 25Mt with an average of about 5Mt, but you can also find giant deposits around 100Mt and up to 150Mt.
SEDEX deposits are dominated by Pb, Zn and Ag with Cu and Au normally being insignificant/absent. Average grades of Pb and Zn in SEDEX deposits is between about 10% and 12% and range between about 3% and 30%.
The average grades of the 9 new holes drilled at Rupice are 7.4% Zn and 4.9%Pb so below average (so far) for a SEDEX.
You have pointed out the Rammelsberg SEDEX deposit as a possible analogue.
Below is a synopsis of that particular deposit.
Rammelsberg is unusual because of its high grade of Cu-Au (1%Cu, 0.5-1.0g/t Au). So far the average grades of Cu and Au at Rupice from the new drill holes is 0.72% Cu and 2.93g/t gold. The gold here is significantly higher and might in itself rule out a SEDEX style deposit. I would need to check as I don't have comprehensive data on SEDEX grades like I do for VMS deposits. The final comment from the summary below (that I've highlighted in bold) points to a genetic link between SEDEX deposits and the Kuroko volcanogenic massive sulfide deposits but if you look at my previous post the Kuroko style VMS deposits are of the Bimodal class and not the pelite-mafic class (ie Besshi -type), so Rammelsberg is a long way from conforming to CSA Global's description above of a possible Besshi-type mineralising environment.
https://e-sga.org/publications/mineral-deposit-archive/the-rammelsberg-deposit/
Summary:
The Rammelsberg Cu-Zn-Pb sulfide-barite deposit in the Harz mountain range, northern Germany, was mined almost continuously for more than a 1000 years (968-1988 AD). The mine, located south of the medieval town centre of Goslar, is now a UNESCO world heritage site. The Rammelsberg is a type locality for shale-hosted, sedimentary-exhalative (SEDEX) Zn-Pb-Ag deposits
but is unusual because of the high grade (27 Mt at 19% Zn, 9% Pb, 160 g/t Ag) and high copper-gold content (1% Cu, 0.5-1 g/t Au) of the sulfide ore.
The Harz is part of the unmetamorphosed slate belt of the Variscan orogen, formed in the Carboniferous during the collision of the paleo-continents Laurussia and Gondwana. The Rammelsberg deposit occurs in a NE-striking, overturned isoclinal syncline of Middle Devonian calcareous black shale, which is enclosed in sand-banded black shale and structurally overlain by Lower Devonian shelf sandstone. In the structural hanging wall but stratigraphic footwall of the sulfide ore, the black shale is altered to a hard quartz-chlorite-ankerite rock termed Kniest. The tightly folded Kniest wedge spans the entire width of the deposit. Pyrite, arsenopyrite and sphalerite disseminations in the Kniest, and sulfide mantos and spotted zones in the Lower Devonian sandstones define a broad zone of epigenetic footwall mineralization. The high-grade massive sulfide, located in the overturned fold limb beneath the Kniest is strongly deformed, recrystallized to a tectonic banding, and separated into two major lenses by reverse movement of the Kniest mass.
The massive sulfide grades laterally into a fringe of shale-banded ore (2 Mt at 6.5% Zn, 3.5% Pb) and is compositionally zoned, stratigraphically higher sulfide-gangue lenses spreading beyond the lower ones. The lowermost lens consists of low-grade pyrite + Fe-dolomite + quartz, overlain by pyrite + Mn-dolomite with layers of chalcopyrite and sphalerite, and blanketed by gold-rich chalcopyrite-sphalerite-galena ore containing 5-10% Fe-dolomite and barite. The uppermost and most extensive layer consists of silver-rich sphalerite-galena ore with intercalated barite beds. Another two beds of sulfide-poor barite occur stratigraphically above the massive sulfide, separated by about 30 m of black shale. Laterally, the sulfide ore grades into the dolomite-rich ore horizon, marked by beds of felsic tuff and traced in drill holes 3 km to the northwest. The ore horizon contains more metal (13 Mt Zn + Pb) than the deposit itself (7-8 Mt Zn + Pb) defining a huge sedimentary-exhalative dispersion halo. The Kniest feeder system, ore textures, and sulfur isotope ratios suggest vent-proximal deposition of sulfide muds in a brine pool by a reduced, H2S-bearing fluid discharging at about 300°C. Radiogenic lead and osmium isotope data indicate deep fluid circulation and metal leaching from the thick pile (>1000 m) of Lower Devonian shelf sandstones and from paragneisses in the continental crust below.
Paleogeographic reconstructions of the Middle Devonian show that the Rammelsberg deposit formed at the faulted margin of an euxinic basin, part of the basin-and-ridge topography of a marine back-arc rift located at the southern margin of the Laurussian continent. Spilitized alkali basalt and trachyte/rhyolite, associated with hematite ore and pyrite mineralization on volcanic ridges, indicate high heat-flow and extensive seawater circulation.
The plate-tectonic setting is remarkably similar to that of the present northwest Pacific, where the Okinawa Trough and the Sea of Japan represent sediment-filled marine rift basins opened in continental crust behind active arc-trench systems. The Japanese Kuroko volcanogenic massive sulfide deposits display ore grades and sulfide-gangue zones almost identical to those of the Rammelsberg, providing a genetic link between VMS and SEDEX, the two main classes of syn-volcanic and syn-sedimentary sulfide deposits.
(20min delay)
