SUMMARY
Firstly, the present development towards a quantitative stereometric (or stereofabric) analysis of mineral aggregates (rocks, ores, concentrates, snow, slags, ceramic materials, cements, etc.) is put into a historic framework. Secondly, the details of the methods and the difficulties still existing are outlined. Finally, a summary is given of the mathematical approaches (with a tabulation of basic formulae), together with some typical examples.
An attempt is made to throw some light on the physical processes in the development of penitentes as a result of new observations in Peru and a study of the literature. This paper offers a variety of approaches to the problem rather than any final view or theory, and is therefore mostly suggestive and intended to be a program for further, more detailed research.
Abstract. The Pataz region in the eastern part of the North Peruvian Department La Libertad hosts a number of important gold mining districts like La Lima, E1 Tingo, Pataz, Parcoy, and Buldibuyo. Economic gold mineralization occurs in quartz-sulfide veins at the margin of the calc-alkaline Pataz Batholith, that mainly consists of granites, granodiorites, and monzodiorites. The batholith is of Paleozoic age and cuts the Precambrian to Early Paleozoic low-grade metamorphic basement series. Its intrusion was controlled by a NNW-trending fault of regional importance. The gold-bearing veins are characterized by a two-stage sulfide mineralization. Bodies of massive pyrite and some arsenopyrite were formed in stage 1, and after subsequent fracturing they served as sites for deposition of gold, electrum, galena, sphalerite, and chalcopyrite. It is concluded that gold was transported as a AuClz-complex by oxidizing chloride solutions and deposited near older pyrite by micro-scale redox changes and a slight temperature decrease. Mineralogical, textural, geochemical, and microthermometric features are interpreted as a consequence of mineralization at considerable depth produced by a hydrothermal system linked with the emplacement of the Pataz Batholith.The Pataz region in the Eastern Cordillera of Northern Peru constitutes one of the major gold-producing zones in the country. Among the few existing geological studies, De Lucio (1905), Tarnaviecki (1929, and Wilson and Reyes (1964) refer to the whole region, whereas Samaniego et al. (1977) and Argtielles and Vidal (1982) deal with certain mining districts. Results of detailed geologic and metallogenetic studies are reported by Lochmann (1985) and Schreiber (1988), Schreiber (1989a and b), andSchreiber et al. (1990 a and b).A series of auriferous quartz-sulfide veins hosted by calc-alkaline plutonic rocks account for most of the extracted gold. The scope of this paper is a synthesis of the essential geologic, geometric, paragenetic, and fluid char-
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