Copper inclusions in sheet silicates from porphyry Cu deposits
Economic geologists have studied the Cu contents of biotite for at least a quarter of a century as potential guides for exploration and as clues to the genesis of porphyry copper deposits1–12. These earlier studies used bulk analytical techniques, and a common, although cautious, assumption was that Cu substituted for Fe in the octahedral sites of the biotite. Here we report data from high-resolution and X-ray analytical transmission electron microscopy which demonstrate that anomalous Cu in biotite is present primarily as submicrometre inclusions of pure native Cu in the interlayer regions of the mica. The inclusions occur with greatest density and size in mixed-layer sheet silicate domains which form by alteration of biotite and chlorite. Less abundant and smaller Cu inclusions are associated with biotites that show subtle alteration only on the high-resolution transmission electron microscopy scale. The association of Cu inclusions with alteration domains, coupled with mass-balance considerations, suggests that these sheet silicates act as Cu sinks, and not as sources for primary mineralization.
Sulfur isotopic composition of thermally metamorphosed cupriferous iron sulfide ores associated with cordierite-anthophyllite rocks, Gull Pond, Newfoundland
Sulfides from the Gull Pond cupriferous iron sulfide deposit of Ordovician (?) age, associated with cordierite-anthophyllite and cordierite-andalusite + or - biotite rocks, show only a limited spread in delta 34 S values: +0.2 to +7.6 per mil with a mean of +4.2 + or - 1.8 per mil. Although the pyrite-pyrrhotite-chalcopyrite-magnetite ores have undergone recrystallization during Devonian thermal metamorphism, sulfur isotopic compositions, especially for pyrite, are considered to reflect original delta 34 S values. Much of the pyrrhotite and some of the magnetite present in the Gull Pond ores were produced during thermal metamorphism. Original ore mineral assemblages at Gull Pond were likely similar to those in ophiolitic cupriferous iron sulfide deposits (Whalesback, Little Bay, Tilt Cove, etc.) elsewhere in Notre Dame Bay (pyrite + or - magnetite) and much of the sulfur in the Gull Pond deposit, like the others, was derived from Ordovician sea-water sulfate.
On the use of the Hardening Soil Small Strain model in geotechnical practice
This article highlights the importance of using advanced constitutive soil models in numerical modelling as daily geotechnical practice. In this context, the Hardening Soil (HS) model is presented as the most advanced soil model implemented in the ZSoil finite element code. The article recalls the basic features of the HS model and it explains their role in numerical simulations. The role of pre-failure non-linear behaviour of soils is also discussed. An application of the HS model is illustrated on typical geotechnical problems such as retaining wall excavation, tunnel excavation and undrained loading followed by consolidation.