34 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



Both the Austrian and ItaHan portions of this region show many deposits 

 of cinnabar, of which not a few have been exploited to some extent. Tlie 

 most famous of the Ttahan mines in this region is the ValLaha, near 

 Agordo.^ The deposit occurs at and near the contact between a mass 

 of quartz porph^-ry and sedimentary rocks of Triassic age, consisting of 

 sandstones, shales, graphitic slate, limestone, and a certain conglomerate. 

 The deposit is irregular in width, but follows the porphyry and ends in 

 strike with this eruptive rock. The cinnabar is found as impregnations in 

 the porphyry and in the sandstone and as stringers in the shales, but the 

 great mass of it is in the conglomerate, which does not seero to be found 

 except in the deposit The matrix of the conglomerate is commonly tal- 

 cose, and embedded in it are rounded pieces of gypsum, calcite, quartz, 

 limestone, and porphyry. Small grains and stringers of cinnabar are scat- 

 tered through the rock. The ordinary material of the deposit contains 

 only two-tenths to 1 per cent, of quicksilver, but the impregnation of cinna- 

 bar increases in some places to such an extent that the greater part of the 

 ground-mass is ore, inclosing fragments of gypsum, calcite, and quartz, as 

 well as foils of magnesian mica. Professor vom Rath estimated the metal- 

 lic contents in such a case, from the specific gravity of the mass, at no less 

 than 24 per cent. The deposit is intersected by numerous veins of cinna- 

 bar, accompanied by seams of gypsum. The only sulphide accompany- 

 ing the ore is pyrite, crystals of which are often embedded in the cinnabar. 

 At the contact between the ore body and the graphitic slate metallic quick- 

 silver was found. Pi'ofessor vom Rath expresses no opinion as to the ori- 

 gin of this deposit, but in the light of what is now know n of the occur- 

 rence of quicksilver I should suppose that the ore had reached its position 

 along a fissure at or near the contact between the porphyry and the adja- 

 cent rocks. The so-called conglomerate Avould seem, from its constituents, 

 to be more strictly a breccia formed by movements prior to the deposition 

 of ore. The precipitation of gypsum and cinnabar nuist have been in part 

 simultaneous, since some of the gypsum is reddened by admixture of ore. 

 The occurrence nf mitivc (juicksilver in contact with graphitic rock (and, so 

 far as reported, there only) is suggestive of reduction. The copper depos- 



'Dcscriljcil by G. vom Katlj : Zeitsclir. I)i utnli. gool. Gesell., vol. 16, IS()4, p. 121, 



