10 AKT. 12. B. KOTO ! 



limestones of various degrees of alteration, and the compact modifi- 

 cation is (lie limc-silicate-hornfels impregnated with sulphide ores and 

 black ilvaitc. 



Microscopically, tiie calcareous rock has an cquigranular, milli- 

 meter-grained, cquant, equiform fabric. 



Cj) The less metamorphosed rock (PL I. figs. 3, 5 and G) contains 

 a little diopside and an uniaxiaP^ serpentine (c parallel to the axis 

 of lamelke). Into the latter the calcite rhomboliedrons project with 

 idiomorphic outline (PI. I. fig. 3, in the right corner). The long 

 prismatic diopside is decomposed into another serpentine, leaving fresh 

 cores like a partially altered olivine (PL I. fig. 5). The diopside is 

 formed first and the serpentine last (fig. 3). Tlie staining method 

 with the Lembeeg solution gives negative results with regard to 

 dolomite or magnesite. A few crystals of chalcopyrite were seen, but 

 none of ilvaite. Tiie rock is properly speaking an opMcalcite. 



Co) The second modification (PL II, figs. 1 and 2) consists of 

 about equal volumes of calcite and contact-metamorphosed minerals. 

 This is impregnated with sulphide ores containing geld, besides diop- 

 side and ilvaite -'. Muscovite is normal. The ilvaite forms acicular 



1) There seem to exist various kinds of serpentines, some occupying an intermediate 

 position between normal serpentines and chlorites. Tlie serpentines are lamellar and antigo- 

 rite-like. 



All the serpentines found in the contact-metamorphosed limestones of the region seem 

 to me to be genetimlUj relaled to the diopside, as may be judged from their modes of occurrence 

 and their transformation from one to the other. This is well seen in PI. I. figs. 3 and 5. lu 

 the former, a prismatic crystal of diopside is seen entirely changed into a serpentinons mineral, 

 and is enclosed in a dlrtij calcite. I could nnt make out why the enclosing calcite has a 

 dirty, weathered aspect in contrast with the mahi muss of crystalline aggregate of the fresh 

 calcite. From their modes of associaiion I can, however, surmise that the fresh anhedra of 

 the calcite are later in the order of crystallization than tlie dirty ones. In the latter (fig. 

 5\ a six-sided crystal of diopside is seen greatly altered into a serpentinons matter 

 leaving some intact cores in the centre and periphery. A similar case is reported to occur in 

 the .sM/7;.-like mass of the contact- metamorph ic deposit of Daschkesan in the Caucasus. 

 Beck: "Lehre von den Erzlagerstätten" Dritte Auflage, S. 153. 



Tiie serpentines are found in such a form that the rocks pres.^nt macrosco;iically an 

 eozoonai stimcture. 



2) The ilvaile-bearing limestones are the ore-body of the Ilol-gol mine. 



A .peculiar paragenetic relation was observed in the course of the examination of the 



