General Metalogenic Concepts Essay

Submitted By gazelle19
Words: 4798
Pages: 20

1

Introduction

1.1 General Metallogenic Concepts

Ore deposits are distributed unevenly on Earth and tend to cluster in specific large-scale zones for which de Launay (1913) introduced the term
"metallogenic province". The observational background for this situation has been known since the earliest days of mining. Pliny the Elder (A.D. 23-79) states with reference to silver-bearing veins: "...ubicumque una inventa vena est, non procul invenitur alia". (Where a vein is found, there will be another one not far away).
Cotta (1859:236) establishes in one of the first textbooks on ore geology the principle: "Wo einmal eine Erzlagerstätte gefunden wurde, da kann man erwarten, unter analogen Verhältnissen auch mehrere derselben oder ähnlicher Art zu finden, denn die meisten von ihnen pflegen gesellig aufzutreten". (Where an ore deposit has been found, it can be expected to find others of similar type under analogous conditions, because most ore deposits tend to occur gregariously). This simple rule is of fundamental importance in exploration geology, condensed in the familiar saying "If you are hunting elephants, go to elephant country".
A further accentuation of the concept of "metallogenic provinces" is derived from the fact that the province-specific metals are sometimes repeatedly concentrated in the same area by different geological processes and at different times, a situation which has been characterized by Routhier (1967) by the notion of "étagement temporel" (temporal superposition). Examples for such situations are given in Routhier (1980).
The existence of metallogenic provinces, i.e., concentration of ore deposits with similar metal-mineral association on a regional scale, points to the control of ore-forming processes by the regional geological framework. The critical role of such large-scale factors is the subject of metallogenic studies. The broader regional approach offers an important supplement to the more usual detailed investigations of individual ore deposits. The focus on detailed relationships within individual ore deposits has yielded critical data about the ores and their genetic processes. The regional approach addresses the broader relationships that link deposits to one another and provides insights

2 into the regional geological environment which causes locally extreme metal concentrations. Broad-scale relationships are per se more complex than relationships on a local scale, which makes quantitative modelling difficult. On the other hand, the regional approach makes it possible to filter from the many individual observations those that are specific for the sum of the ore deposits in a given metallogenic province, and that can be regarded as critical factors for ore formation in general.
The observational background of each student of ore deposits is, of course, different. This may introduce a subjective factor into any judgement of a complex sum of individual observations. The acquisition of general principles from a large data set relies on extra-observational background knowledge and the partly intuitive notion of relevance, about which different people may have different ideas. This is the reason for the diversity in metallogenic concepts dealing with identical subjects.
The existence of metallogenic provinces has been interpreted by Schuiling
(1967:540) as reflecting a regional geochemical anomaly: "The concept of a metallogenetic province implies the existence of large-scale chemical inhomogeneities in that part of the crust or the mantle from which the ore deposits ultimately were derived".
This statement extends the neutral notion of metallogenic province to the speculative concepts of geochemical province, regional geochemical specialization and metal domain (Routhier 1967). It has been developed by
Routhier (1980:46) into the "basic theorem" of metallogeny: "The concentrations of a metal appear at the intersection of a metal…