This paper presents U-Pb-He triple-dating age detenninations for several porphyry Cu±Mo+Au deposits in Chile, Indonesia and Iran in an effort to determine their thermal histories and to explore the effects of cooling/exhumation rates on ore formation and preservation processes. Inverse thermal modelling of measured time-temperature history data from these deposits was conducted to quantitatively constrain the depth of emplacement, duration of ore deposition, exposure ages and cooling/exhumation rates. The duration of hypogene ore formation for the deposits studied generally occurs within timeframes of 105 years, although modelling results for the Grasberg, Batu Hijau and El Teniente super porphyry deposits suggest formation periods of the order of 104 years. Emplacement depths on intrusions associated with porphyry mineralisation range from 800 m to 5500 m from the palaeosurface, with Grasberg and Rio Blanco being respectively the shallowest and deepest super porphyry deposits studied. The thermochronology data indicates a positive correlation between metal grade and cooling rate during hypogene ore formation, but further investigation is warranted. Exhumation rates varying from 0.3 to 1.1 km/m.y. have implications for the preservation potential of hypogene ore deposits, with super porphyry deposits like Sar Cheshmeh potentially losing 3.5 Mt of copper to erosion over the last 5 million years. The potential for supergene ore formation under such conditions is high, as is the potential for the formation of proximal Exotica-type deposits.

The geometry and distribution of the clastic dv s.es of the Ono district. North Sacramento Valley are examined within stream sections. Five traverses along dry stream beds provide good exposure allowing the spacing, thickness and geometry of the dykes to be reorded. The spatial and thickness distribution of the dykes are considered using cumulative frequency plots, allowing a visual estimation of a best lit distribution. Dyke thickness conforms best to a log-normal distribution. There is also a characteristic minimum dyke thickness in a traverse and this is attributed lo the minimum aperture thai a fluid with sand clasts is able to exploit. Dyke spacing, however, shows a good correlation with a power-law distribution for four traverses, suggesting thai there is a mechanistic control on the spatial dislribulion. Plolting dyke thickness against minimum dyke spacing reveals that thin dykes do not generally intrude in isolation. I'nlike veins and igneous dykes, elastic dykes continue lo provide preferential pathways for fluid flow, subsequent lo their intrusion, thus inhibiting intrusion in the area surrounding a pre-existing dyke. Acombination of this process and dyke branching provides the best model for the observed spatial and thickness distribution of clastic dykes seen in the Ono district. California.

In the early 1960s, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Since then, scientists have verified and refined this theory, and now have a much better understanding of how our planet has been shaped by plate-tectonic processes. We now know that, directly or indirectly, plate tectonics influences nearly all geologic processes, past and present. Indeed, the notion that the entire Earth's surface is continually shifting has profoundly changed the way we view our world. <...>

Anisotropic and foliated rock masses, the behaviour of which are dominated by closely spaced planes of weakness, present particular difficulties in the assessment of pit slope stability. Various numerical modelling techniques are available that explicitly simulate the joints and discontinuities within an anisotropic rock mass. However, due to the computational intensity of these numerical techniques, it is not practical to explicitly simulate the joint fabric of an entire three-dimensional pit slope for routine stability assessment. In order to simulate the effects of anisotropic rock mass strength and deformation behaviour on pit slope stability, a modelling methodology has been developed to account for rock mass anisotropy and scale effects using a continuum based ubiquitous joint constitutive model. This paper outlines the anisotropic modelling methodology and presents a series of demonstration models that have been used to validate the technique.  <...>