METAMORPHISM AND SUPERGENE ALTERATION OF
Four principal types of sulfide ore are recognized at the Thiegry'mine, located in the Uchi volcanic belt (Superior Province), northwestern Ontario. These are: disseminated Cu-Ni-Fe sulfides, breccia ore, mylonite ore and bornite ore. The sulfides are interpreted to be of magmatic origin, but modified by strong shearing to produce mylonite and breccia ore. The bornite ore represents enrichment in Cu of blocks of amphibolite schist in the mylonite. Supergene alteration removed iron from the iron-nickel sulfides to produce iron oxides and sulfides, especially violarite enriched in cobalt and nickel. Violarite (Ni-Fe-rich) appears to coexist with pentlandite where it formed from pentlandite. Violarite (Ni-Co-rich) generated as the result of metamorphism does not coedst with pentlandite. This strongly suggests that cobalt plays a major role in defining the lowtemperature stability fields and explains the two conflicting interpretations of assemblages involving violarite in the system Fe-Ni-S. The modification, during deformation and metamorphism, of primary magmatic sulfides of subeconomic grade to an ore deposit at Thierry and other areas implies that an ulfiamafic-gabbroic body in an intensely metamorphosed and deformed terrane might offer a better target for er<ploration than ore in lower-grade rocks. Furthermore, the enrichment of platinum-group elements @GE) in mylonite and bornite ores at Thierry indicates that mobilization into shear zones could produce PGE deposits.
Mineralogy of the Marbridge No. 3 & No. 4 nickel-iron sulfide deposits; with some comments on low temperature equilibration in the Fe-Ni-S system
The Marbridge No. 3 and 4 deposits are associated with lens-like bodies of serpentinized ultramafic rock that occur within a sequence of interbanded felsic volcanic rocks and graywackes. Both deposits consist of sulfide disseminated within the host peridotite, together with smaller amounts of stringer ore. Ore at the No. 3 deposit occurs towards the top of its associated serpentinite while that at the No. 4 occurs towards the base.The major sulfide minerals at the No. 4 deposit are pyrite and pentlandite together with minor amounts of millerite. At No. 3, the ore is zoned parallel to the contact with the host volcanics. The major part consists of pyrite, pentlandite and millerite, but close to the contact the assemblage pyrite-pentlandite-pyrrhotite is developed. Small amounts of pentlandite and heazlewoodite occur at the center of the serpentinite lens at the No. 3 deposit. Pentlandite is extensively altered to violarite throughout much of this deposit.Electron microprobe analyses of pentlandite from the Marbridge deposits, together with samples from the Alexo mine, the Texmont mine and the Sudbury ores indicate that the Fe:(Ni + Fe) ratio of pentlandite varies directly with the minerals with which it is associated, ranging from 0.518 for that in association with troilite and intermediate hexagonal pyrrhotite to 0.341 in association with heazlewoodite. This relationship indicates that equilibrium has been established between pentlandite and its associated minerals and is supporting evidence for the existence of a stable tie-line between pentlandite and pyrite at low temperatures in the Fe-Ni-S system.
The Inca Occupation of the South Coast of Peru
like the others, however; it forks into several nearly parallel ravines of which the largest are Huayuri, Rio Grande-Palpa, Ingenio (called Collao in ancient times), Nasca proper (the ancient Caxamarca), Taruga, and Poroma. Due to peculiarities of the local topography, the irrigated areas in Ica and the ravines of Nasca are located inland, at the foot of the mountains, rather than at the mouths of the rivers as is more usual in Peruvian coastal valleys. No sharp natural or cultural boundary separates the valley of Chincha from the valleys of Cafiete (ancient Huarco and Runahuana), Asia, and Mala, the next valleys going up the coast to the northwest. At the other end of the area we are considering, however, there is a sharp break; beyond Yauca the Andean foothills reach out to the sea, natural conditions are quite different, and there are important differences in the archaeological picture as well. The historical sources which mention the south coast are not particularly helpful, except in so far as they provide us with a few dates. To begin with, no chronicler gives an explicit account of the political organization of the south coast at the time it came into contact with the Incas. It can, perhaps, be inferred from Cabello Balboa's statements about common policy toward the Inca invaders that there was some sort of political connection between the valleys of Mala, Cafiete, and Chincha, but the connection need have been no more than a temporary military alliance. Cabello makes no mention at all of Pisco. The valleys of Ica, Nasca, and 125