World's Largest Ore Research Articles

Effects of fluorine on dynamic reaction interfaces in hydrothermal feldspar alteration

Fluid-induced mineral reactions exert an important control on the physico-chemical properties of the crust and hydrothermal plumbing systems. Feldspars are the most abundant minerals in the Earth's crust and a major host of the main cations found in geofluids (Na, K, Ca). In previous work, we discovered that K-feldspar-albite-sanidine zonation textures developed dynamically when sanidine ((K,Na)AlSi3O8) was reacted with NaCl or NaF in H216O- and H218O-enriched solutions at 600 °C and 2 kbar in a closed system. Based on a detailed SEM and TEM characterisation, the present study aims to constrain the reaction mechanism and the effect of fluorine on reaction kinetics and overall reaction textures in alkali feldspar replacement reaction interfaces. Replacement of high-sanidine (Sa) by albite (Ab) and/or K-feldspar (Kfs) proceeded via an interface-coupled dissolution-reprecipitation reaction, with the products preserving the crystallographic orientation of the parent Sa in both NaCl- and NaF-bearing solutions. Mineral interfaces with different micro-textures were observed depending on the nature of the interface (Ab-Sa, Kfs-Ab, Kfs-Sa) and whether the reaction occurred in NaCl-only or NaF-bearing solutions. Abundant amorphous domains (25–50 nm thick) occur both within Ab and at Ab-Sa and Kfs-Ab interfaces formed in NaF-bearing solutions. At the Kfs-Sa interface formed in NaCl-only solutions, a complex interfacial zone characterised by a high density of defects may represent sealed fluid pathways. These results reveal that the nature of the reaction interface depends on both mineral properties, in particular microtextures (i.e. polysynthetic twinning in Ab); and solution chemistry; this directly affects porosity development, the chemical environment at the interface, and chemical exchanges between the reaction front and the bulk solution. Fluorine aids the formation of amorphous layers that modify nucleation mechanisms; and facilitates element transport by forming Na-Si-Al-fluoride complexes, resulting in accelerated reaction rates relative to chloride-solutions. These nm- to μm-level processes contribute to efficient coupling between fluid-flow and mass transfer, explaining why sodic and potassic alteration associated with metal and fluid transport in some of the world's largest ore deposits can develop extensively, and subsequently access metals locked within silicate mineral assemblages.

Geochronology of the Iberian Pyrite Belt and the Sierra Norte Batholith: lower plate magmatism during supercontinent amalgamation?

Abstract Protracted magmatism has long been recognized in the exotic South Portuguese Zone of southern Iberia where Early–Late Devonian volcano-sedimentary successions potentially record processes associated with ocean closure and continental collision associated with the formation of Pangaea. Collectively, these rocks represent a bimodal, predominantly submarine volcanic succession with massive sulfides spatially associated with basalts and rhyolites. Volcanic rocks are intruded by the voluminous Sierra Norte Batholith. Although the region hosts some of the world's largest ore deposits, the temporal and genetic relationships between the Iberian Pyrite Belt, the Sierra Norte Batholith and the evolution of the Variscan Orogen remain enigmatic. In an attempt to better understand these complexities, field investigations and targeted geochronology were completed throughout the volcanic and sedimentary rocks of the Iberian Pyrite Belt, and the plutonic rocks of the proximal Sierra Norte Batholith. Our results suggest that the emplacement of the pyrite belt was both pre- and syncollisional, and was initiated primarily by lithospheric delamination related to tectonic escape and crustal thinning of the lower plate. In this scenario, protracted magmatism occurred in both subaerial and subaqueous settings from c. 370 to 338 Ma.

The Iron Ore Industry of Canada

EVERYONE WHO IS INTERESTED in the future of the American steel industry-and that really means everyone who is interested in the future of this countryshould be aware of the implications of Canada's emergence as one of the world's great iron ore producers. In 1939 there was no iron ore production in Canada proper, and had been none for 15 years. In 1956, Canada was the fourth largest ore producer in the world, and is just now beginning to hit its stride. The promise of a great Canadian iron ore industry which has been implicit for more than 60 years-ever since the classic explorations of A. P. Low, in the Labrador Trough late in the nineteenth century-is now becoming a reality. For as far into the future as anyone can see, Canada should continue to be a major producer. But every producer needs a customer, or several customers, and Canada has one right next door in the United States as well as her own growing steel producers. Already by far the world's largest iron ore consuming nation, we will soon be the world's largest ore importer as our steel production continues to rise. It is the existence of this market-and, to an increasing degree, the needs of Western Europe's steel industrythat will allow Canada's mining industry to reach its fullest and most profitable development. All this is really just another way of saying that Canada has an abundance of iron ore-more than it can use at home now, more than it can use at home any time in the foreseeable future, even recognizing the vigorous expansion of the Canadian steel industry which is now taking place. Last year, Canada produced approximately 17 million long tons of ore, 12 million of it from the newly developed Quebec-Labrador Range. Approximately 90% of the total was exported, principally to the United States, but also to Western Europe and Japan. Recently a study of probable production and consumption of iron ore around the world between now and 1980 was made. Parenthetically, let me remind you that if there is one generalization that can be made about forecasts on steel production or iron ore consumption it is this: in the last 15 years, they have universally been too low. This could well be the case with the figure I am going to quote to you now. It is estimated that by 1960 Canada will be producing approximately 20 million long tons of iron ore a year. By 1965 this could rise to 25 million tons; by 1970 to 30 million tons; by 1975 to 45 million tons; and by 1980 to 55 million tons. Such figures are indicative of a trend as everyone must realize that historically steel expansion goes in waves. Now, 55 million tons is a lot of iron ore. Before the war, which touched off 15 years unabated demand for steel, we considered it a lot for this country to produce. Iron ore mining, therefore, is certain to bulk very large in the over-all Canadian economy. THE HISTORY OF CANADIAN ORE