Geology Reference
In-Depth Information
Figure 10.6
Chromatite layers in two Rivers Mine, Bushveld, South Africa.
example the Borrowdale Volcanic Group at Sellafield in the UK or Yucca
Mountain in Nevada, USA).
iii) Hydrocarbon potential. This may come as much of a surprise to igneous
petrologists as petroleum geologists, but igneous rocks can and do act as
hydrocarbon reservoirs. Several highly productive plays in South East Asia
are extracting oil and gas directly from drilling fractured igneous reservoirs
(referred to generically as 'basement' by petroleum engineers). As non-
traditional sources dry up, these so-called exotic reservoirs may gain more
prominence.
iv) Volcano instability. Studies over the last decade have helped raise awareness
of the life and property threatening hazards that result from volcano insta-
bility and collapse. Understanding the processes behind catastrophic edifice
failure, and mitigating the associated risks, requires knowing about the phys-
ical properties, strength and cohesion of the rock mass comprising a volcano.
In the sections that follow, we introduce the key concepts of rock mass
strength, intact rock strength, friction, cohesion and show how using simple field
estimates it is possible to make some clear predictions on the overall strength
properties of igneous rocks in the field as a first step towards a more detailed
examination of their geotechnical properties using, for example numerical
simulations. We focus here on the rock mass classification of volcanic rocks
but note the same principles apply to plutonic rocks regardless of composition.
