“Fluorite deposits at Encantada-Buenavista, Mexico: products of Mississippi Valley type processes” [Ore Geol. Rev. 23 (2003), 107–124]—a reply

Abstract

We very much appreciate the comments of Dr.Spirakis regarding the fluorite deposits of La Encan-tada-Buenavista. The contribution by Gonza´lez-Par-tida et al. (2003) represents a partial report of thework we are carrying out on the fluorite deposits ofnorthern Coahuila State (Mexico). We have subse-quently conducted further work on the deposit inorder to complement the information already pub-lished, addressing controls on the distribution of themineralized bodies and halogen studies of fluid inclu-sions. We discuss here, in light of our new results, theproblem of fluorine transport and precipitation at LaEncantada-Buenavista.New developments in the mine showed that there isa strong structural control on the distribution offluorite bodies. The latter are found at the intersectionof low-permeability barriers, with low angle faults(layer-parallel slip) developed at stratification bound-aries with abundant clayey materials. Precipitation offluorite is preceded by a dramatic increase in perme-ability due to the hydraulic fracturing of the host rock.Enclosing rock fragments included in the newlydeveloped breccias are usually recrystallized andslightly corroded, but are also rapidly covered byfluorite, the precipitation of which appears to precludethe continuance of carbonate replacement. A thincalcite blanket, typically a few centimeters to deci-meters thick, is found at the boundary of the fluoritebody smoothly passing to the slightly recrystallizedenclosing limestone. Fluorite appears as white tocolorless, corrosion-free crystals indicative of passivemineral precipitation. Late cavities are filled up byidiomorphic, cubic, zoned fluorite crystals with adeep-purple color in their outer zones, minor idiomor-phic calcite scalenoedrons and extremely rare crystalsof barite.