Alkaline-Related Gold Systems: An Overview
What is an alkaline-related gold system? How to tell it apart from other auriferous mineralizations? Why is it important?
Below, I present a brief introduction of the alkaline gold system, highlighting its salient characteristics.
In picking gold mining stocks, investors should recognize the implications of potential occurrence of alkaline-related gold mineralization.
Alkaline-related epithermal to porphyry gold is one of the most important types of auriferous mineralization types. Some of the largest gold-copper mines actually are actually alkaline-related, from Cripple Creek and Sierra Blanca in North America, via Olympic Dam in Australia, to Grasberg, Porgera, and Emperor in Australasia (Fig. 1).
Fig. 1. Spatial distribution of alkaline-related gold districts. Source.
In a recent Seeking Alpha roundtable discussion entitled "Getting Past The Headlines For Gold And Energy", I recommended Lion One Metals (OTCQX:LOMLF) partly because of its alkaline gold potential, by stating the following,
At this time, we like Lion One Metals a lot, which operates in Fiji, part of the ring of fire where numerous giant gold mines are found. The company is poised to pour first gold in 2020, providing it with cash flow. On the other hand, the exploration upside in its Tuvatu concessions - not only in shallow epithermal targets but also in deep alkaline porphyry gold prospects as it recently recognized - can potentially multiply its high-grade gold resource. So this is a barbell investment play. The miner is run by Wally Berukoff, a serially-successful entrepreneur and major shareholder. The stock, currently consolidating after a bounce off the bottom in January 2019, is still deeply undervalued.
I received inquiries about that gold miner in particular and about alkaline gold mineralization in general. Below, I would like to give alkaline gold systems a brief introduction, to set the stage for an in-depth examination of Lion One Metals.
Alkaline gold systems
Studies indicate alkaline gold systems fall into two main categories, i.e., relatively low-temperature, shallow (<1-2 km), epithermal-style deposits and high-temperature, variable depth (>1 km), porphyry-style deposits (Fig. 2). A number of districts contain both styles of deposits.
Fig. 2. Grade-tonnage plot for alkaline-related gold deposits, with dashed contour indicating total gold in deposit and shaded area defining field for >80% lode veins. Cripple Creek is plotted as three dots, i.e., La Plata Mts historical high-grade epithermal veins, Cripple Creek I high-grade veins system, and Cripple Creek II low-grade 'disseminated' deposits. Source.
In alkaline epithermal deposits,
mineralization is mainly in the form of telluride-rich gold veins that contain varying proportions of quartz, carbonate, adularia, and sulfates. Most veins have low total sulfides, poor in copper and molybdenum, and more gold than silver. Potassium metasomatism is described in nearly all alkaline epithermal deposits, either in the form of sericitic or adularia-sericite alteration. Tellurium and vanadium are likely reliable pathfinder elements for distinguishing alkaline-related mineralization from other types of epithermal gold deposits.A transition between alkaline epithermal and porphyry deposits are observed; epithermal deposits with grading downward into or overprinting porphyry-type copper-gold deposits.
In alkaline porphyry deposits,
mineralization is either copper-rich or molybdenum-rich, associated with mafic to intermediate or felsic magmatism, respectively. Copper mineralization is typically characterized by a zone containing central bornite and magnetite that grades outward to bornite + chalcopyrite and chalcopyrite + pyrite. Gold mineralization occurs as native gold, tellurides, cuprian gold, or auriferous sulfides, and is usually found in bornite-rich zones. Tellurides are much less than in the shallow epithermal systems. Gold to silver ratio is much lower in alkaline porphyry systems than in alkaline epithermal systems. Alteration includes potassium, sodium, propylitic, and magnetite replacement (Fig. 3).
Fig. 3. Schematic illustration of the relationship between magmatic intrusive rocks, host rocks, and metal distribution in alkaline-related gold deposits.
Alkaline-related deposits can be particularly attractive for environmental and metallurgical reasons thanks to their feldspar and carbonate-rich alteration and low sulfide total concentrations.
Investor takeaways
Investors interested in gold investing (GLD) should recognize the importance of alkaline-related auriferous mineralization, alongside Archean greenstone belts, sediment-hosted gold systems, and others.
Alkaline-related gold systems are known not only for their high-grade and large tonnage but also for their low-sulfide mineralogy, which happens to have beneficial metallurgical and environmental implications.
Some alkaline epithermal gold deposits found in the shallow levels may just be the tip of an iceberg so to speak, because there may exist much larger, alkaline porphyry gold systems in the depths. Such is suspected to be the case for Lion One Metals, which of course is the topic of another article.
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Disclosure: I am/we are long LOMLF. I wrote this article myself, and it expresses my own opinions. I am not receiving compensation for it (other than from Seeking Alpha). I have no business relationship with any company whose stock is mentioned in this article.
Editor's Note: This article covers one or more microcap stocks. Please be aware of the risks associated with these stocks.
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