Conceptual Methods for Modelling Systems of Mineralized Echelon Veins: Examples from Southwest England and Portuga
Exploration & Mining Geology, Vol. 4, No. 3, 1995
K.A. FOXFORD*, R. NICHOLSON, Geology Department, The University of Manchester, Manchester, M13 9PL, United Kingdom. R.P.B. HEBBLETHWAITE Consulting Geologist, The Coach House, Blackwell Hall Lane, Latimer, Nr Chesham, Bucks, HP5 1TN, United Kingdom
Geology Department, The University of Manchester, Manchester, M13 9PL, United Kingdo
A variety of techniques for interpreting systems of mineralized echelon
veins is discussed using examples from Panasqueira and SW England. As aids for
exploration and mine planning, and as a tool for ore reserve evaluation,
particular emphasis is placed upon establishing vein morphology in the third
dimension, and upon understanding vein dilation and propagation histories.
Special attention is also placed upon investigating vein thickness and spacing
relationships, and upon understanding vein segmentation. The relevant data for
these techniques are all readily obtainable from stope and core sources. The
vein systems described were produced in host-rock sequences that underwent
incremental dilation in response to ?uid overpressures, and individual veins
display evidence for mineral in?lling synchronous with their propagation.
Echelon vein geometries resemble those reported from igneous dikes and sills:
vein walls are stepped and veins are divided into segments arranged in echelons.
Changes in vein geometry, from arrays to composite structures, re?ect both the
evolution of the vein system with time, and the changes occurring between the
margins (arrays) and core (composite structures) of the system. These
characteristic morphologies can be used to infer vein propagation and ?uid
injection trends, proximity of neighboring veins, and the shape of the system as
a whole. The techniques are applicable to systems of echelon veins produced
under tensile conditions in rocks where faults were absent at the time of vein
formation, and where subsequent deformation has been minimal. Further work is
required to assess the application to echelon vein systems formed within more
complex tectonic regimes.
Modelling Systems,Mineralized echelon veins, Vein systems, Vein dialation