BRECCIAS : PROCESS OF BRECCIA ANALYSIS, DESCRIPTIVE TERMINOLOGY, COLLOQUIAL TERMINOLOGY,GENETIC TERMINOLOGY, CONCLUSIONS AND EXPLORATION IMPLORATIONS

BRECCIAS : PROCESS OF BRECCIA ANALYSIS, DESCRIPTIVE TERMINOLOGY, COLLOQUIAL TERMINOLOGY,GENETIC TERMINOLOGY, CONCLUSIONS AND EXPLORATION IMPLORATIONS

Corbett Short Course Manual

Breccias are broken rocks studied for their variable relationship to mineralisation, including as vectors to ore, although there are a myriad of breccia forms and modes of breccia development. Explorationists must therefore be able to distinguish different breccias and apply names to them as a means to access the exploration significance of many breccias, which occur throughout the geological record occupied by epithermal and porphyry deposits. While pre- existing volcanic breccias (McPhee et al., 1993) and to a lesser extent clastic sedimentary rocks (Petijohn, 1975) may host later mineralisation, breccias dealt with in epithermal-porphyry exploration are derived from an interaction of hydrothermal-structural- magmatic–volcanic processes (Davies et al., 2000) as well as local carbonate dissolution. The challenge for explorationists is to provide an efficient breccia

nomenclature which will enable us map breccias and to communicate field studies to our peers, some of whom will have different ideas on breccias. While Roger Taylor (2009) points out the difficulty of

breccia nomenclature, noting the 832 page effort by Laznicka (1988), explorationists might benefit from earlier discussions of ore-related breccias by Sillitoe, (1985), Baker et al., (1986), Taylor and Pollard (1993), Corbett and Leach, (1998), Davies et al., (2000) and Taylor (2009), which this discussion draws on.

Consequently, from the author’s field experience and reference to published studies three means of breccia nomenclature might be considered:

  • Descriptive breccia terminology based upon the appearance of the breccia using characteristics set out by McPhee et al. (1993) for volcanic breccias and applied by Davies et al. (2000) to porphyry and epithermal deposits.

• Colloquial breccia terminology as terms developed through common use (Corbett, short courses; Taylor, 2009).

• Genetic breccia terminology based upon the means of formation (Sillitoe, 1985; Corbett and Leach, 1998; Pollard and Taylor, 1993).

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