Распределение халькофильных элементов и элементов платиновой группы в ультраосновных породах комплекса Стиллуотер, Массачусетс, США - влияние на процессы обогащения слоев хромита Os, Ir, Ru и Rh

All of the rocks from the Ultramafic series of the Stillwater Complex are enriched in PGE relative to most mafic magmas. Furthermore, the chromite layers are particularly enriched in IPGE (Os, Ir, and Ru) and Rh. This enrichment appears to be a common characteristic of ultramafic rocks from many types of settings, layered intrusions, ophiolites, and zoned complexes.

The geology of northwestern Mexico is complex and is similar in many respects to that of southeastern California and southern Arizona. The region (Fig. 1), typical of the southern basin-and-range physiographic province of which it is a part, is characterized by elongate, northwest-trending ranges separated by wide alluvial valleys. Basement rocks in the area include Precambrian gneisses, metamorphosed andes-ites, and granites. These rocks are overlain by younger Proterozoic quartzites and limestones, Paleozoic and Mesozoic carbonate rocks, and Mesozoic volcanic, clastic, and carbonate sedimentary rocks. Mesozoic plutonic rocks and Tertiary extrusive and intrusive rocks related to volcanic activity of the Sierra Madre Occidental are widely distributed. Broad areas are underlain by plutonic and associated volcanic rocks of the Sonora-Sinaloabatholith of Cretaceous to early Tertiary (Laramide) age. The outcrop areas of the plutonic rocks are smaller in northwestern Sonora, west of Magdalena de Kino where many of the gold deposits are concentrated, than they are farther to the east and south (Fig. 2).

Wilson and Parry (1995) present data pertaining to clay alteration and K-Ar age dates for samples from the Mercur gold district. Their data record a wide spread of K-Ar ages for illite ranging from 98.4 to 226 Ma. They estimate the age of gold mineralization to be between 140 and 160 Ma and explain the wide range of ages as functions of partial thermal resetting of the clay minerals and the distance from the hydrothermal conduits. Morris and Tooker (1996) in their discussion of this paper, point out that a Mesozoic age for gold mineralization at Mercur is incompatible with several lines of long-standing regional geologic evidence that suggest a Tertiary age. In their reply, Wilson and Parry (1996) defend their position for a Mesozoic age of mineralization in part by relying on new 40Ar/39Ar age data and the fact that none of the 22 age dates is Tertiary. Although the research by Wilson and Parry may represent a good study of samples in the laboratory, there are several tenuous assumptions and contradictions of the geologic observations at Mercur that must be addressed.

L’étude des sols latéritiques de la région de l’Agnéby en Côte d’Ivoire a été effectuée sur les données géotechniques des rapports d’étude de dix sections de routes construites en utilisant des graveleux latéritiques dans la structure de chaussée. Ces donné escomportaient des courbes granulométriques, des limites de consistance pour la fraction fine, des résultats d’essais Proctor modifié et d’essais CBR.