The Origin of Epigenetic Gold Deposits—the Ore-Magma Theory

Abstract

Before proceeding to the main part of this chapter it should he recalled that four general theories for the origin of vein-type gold deposits had been postulated by the midnineteenth century: the ore-magma theory involving siliceous melts, the magmatic-hydrothermal theory, secretion theories, and abyssal theories. The ultimate source of the gold, other metals, and gangue elements (minerals) in gold deposits is mentioned only briefly in these early theories and usually with little elaboration. It was generally assumed that the magmas, the basic materials of the first two theories, were developed by some process involving the melting (granitization) of preexisting crustal rocks, generally sediments, although some early investigators allude to melting of deeper rocks (the mantle?). How the magmas became enriched in gold (and other metals) was usually not mentioned, and indeed today the details are still bypassed by most writers on the subject. The secretionists placed the source of the gold (and other metals) in the host rocks of the deposits, some in the rocks immediately enveloping the deposits (lateral secretion), and others in the general piles of sediments and volcanics hosting the deposits (diagenetic and metamorphic secretion). Advocates of abyssal theories relegated the source of the gold and other metallic vapors, solutions, or melts to the great depths of the earth, often to deep-seated metallic, sulfidic, or other mineral spheres far below the plane of observation.

The igneous theory is sufficient to account for the primary forms and the arrangements of minerals in lodes. Thomas Belt, 1861