Economic Geology

Dating of alteration at the Radomiro Tomic porphyry copper deposit, northern Chile by the high precision (super 40) Ar/ (super 39) Ar method

by Greg Pemberton

Marcos Zentilli: http://ca.linkedin.com/in/marcoszentilli

Dating of alteration at the Radomiro Tomic Porphyry Copper Deposit, northern Chile by the high precision 40Ar/39Ar... more Dating of alteration at the Radomiro Tomic Porphyry Copper Deposit, northern Chile by the high precision 40Ar/39Ar method

Gregory Pemberton

The Radomiro Tomic (RT) porphyry copper deposit is located approximately 8-10km north of the Chuquicamata mine and 245km northeast of the port city of Antofagasta. Estimates place the deposit at over 800 million tonnes of ore with an average grade of 0.59% Cu (mostly supergene ore) and a mine life of 22 years. RT does not outcrop as the entire deposit is buried beneath Miocene piedmont gravels up to 200m in thickness and has been known only from drillcore and limited underground workings. Stripping is now underway and the mine is due to start operating in 1997 as a new separate division of CODELCO, the Chilean national copper mining company.

The deposit is hosted within an intrusive body of quartz monzodiorite composition that is approximately lower to middle Oligocene in age and was emplaced within the regional N-S trending Domeyko Fault system. This system is spatially associated with all the major porphyry deposits in northern Chile.

High precision, stepwise degassing 40Ar/39Ar dating was conducted at Dalhousie University to determine the ages of the potassic, argillic and quartz-sericite alteration assemblages at Radomiro Tomic. K-feldspar, biotite and sericite grains were hand picked from six drillcore samples representing the three hydrothermal alteration zones. Results are suggestive of potassic and argillic alteration assemblages having an average age of 32.6±0.3Ma as part of an initial hydrothermal event. As well, a younger hydrothermal event was dated to 31.8±0.3Ma from quartz-sericitic alteration minerals. Age differences among the potassic and argillic alteration minerals (K-feldspar and biotite) having high or low closure temperatures are not detectable, are indicative of rapid cooling following emplacement of the host porphyry. 39Ar degassing plateau patterns combined with X-ray diffraction analyses on the K-feldspar samples also support the scenario of a rapid decrease in temperature to less than 150oC in the order of hundreds of thousands of years, rather than millions, following each hydrothermal event.

A full suite of ancillary data was generated on the dated samples establishing the close similarity of the petrology, mineralogy and chemistry to samples of similar alteration types from Chuquicamata.

Key Words and Phrases: Radomiro Tomic, porphyry copper deposit, Chile, argon dating, geochronology, hydrothermal, alteration, potassic, argillic, quartz-sericitic, Chuquicamata

Pemberton, G.B., 1997,'The Geochronology of the Radomiro Tomic Porphyry Copper Deposit, Northern Chile', Atlantic Geology, V33, 1, pp73-74

Supervisor: M Zentilli

Mid-Cretaceous crustal extension recorded in deep-marine half-graben fill, Cedros Island

by Cathy Busby

Smith, D. P., and Busby, C. J., 1993a, Mid-Cretaceous crustal extension recorded in deep-marine half-graben fill, Cedros Island, Mexico.  Geol. Soc. America Bull., v. 105, p. 547-562.

Volcanic setting of the Ordovician Bald Mountain Massive Sulfide Deposit, Northern Maine

by Cathy Busby

Busby, C.J., Kessel, L., Schulz, K., Foose, M., and Slack, J., 2003, Volcanic setting of the Ordovician Bald Mountain Massive Sulfide Deposit, Northern Maine: in, W. Goodfellow, S.R.McCutcheon and J.M. Peter (eds.), Massive Sulfide Deposits of the Bathurst Mining Camp, New Brunswick and Northern Maine:  Economic Geology Monograph 11, p. 219-244 plus 2 large plates in back pocket

Empowering geoscientists with entrepreneurial skills – bring back the ‘economics’ in economic geology course

by Emmanuel Igonor

Igonor E.E. and Oden, M.I.

Unemployment is on a steady increase and the probability of getting a job is on a steady decline. This unemployment... more Unemployment is on a steady increase and the probability of getting a job is on a steady decline. This unemployment has caused serious economic and financial crisis, which is not restricted to the poor or developing nations of the world but has also affected the developed nations. Global trends report of 2011 shows that the global unemployment-to-population ratio declined from 61.7 in 2007 to 61.1 in 2010. Also the number of countries with falling employment-to-population ratio was still twice the number that had rising ratios. The youths are the worst hit by this, as the global youth unemployment rate stood at 12.6% in 2010, an increase from 11.8% in 2007. The geosciences sector is not exempted from this global crisis. The pending retirement of professionals and the uncertainty regarding the adequacy of this replacement with respect to quantity and quality is a major concern. This work looks at the possibility of empowering geoscientists with entrepreneurship skills to combat unemployment. Research results show that entrepreneurial skills and training is so much needed today to empower geoscientists. And the easiest means is when the ‘economics’ in ‘economic geology’ is brought back. The policy makers and geoscientists/geosciences students must all work together to see that the true elements of economics – business, trade, money, and industry is re-introduced fully into the teaching of economic geology course, as this is the fastest way to generate interest and alertness to the whole geosciences education and ensure the production of qualitative and quantitative geoscientists to replace the ageing and retiring ones. In other words, the geosciences education needs to be ‘monetized’. So the ‘economics’ of economic geology course must be brought back.

Minería submarina: se inicia la explotación de los fondos oceánicos

by F. Javier González Sanz

Somoza, L., González, F.J., 2011. Minería submarina: se inicia la explotación de los fondos oceánicos. Enseñanza de las Ciencias de la Tierra 19 (1), 115-118.

Los océanos cubren casi las tres cuartas partes de la superficie de la Tierra, contienen las nueve décimas partes de... more Los océanos cubren casi las tres cuartas partes de la superficie de la Tierra, contienen las nueve décimas partes de los recursos de agua y más del 97% de los seres vivos del planeta. Los océanos son parte esencial de nuestra biosfera: influyen en nuestro clima y afectan a nuestra salud y nuestro bienestar. Los océanos están dominados por fondos profundos ya que más del 60% de la superficie del planeta está por debajo de los 2.000 metros de profundidad.
Los recursos energéticos y minerales que se pueden encontrar en los fondos marinos profundos incluyen petróleo, gas natural, hidratos de gas, nódulos de manganeso, costras ricas en cobalto, sulfuros masivos (ricos en zinc, plata, oro o cobre), fosforitas, áridos (arena y gravas) y placeres (ricos en titanio, tierras raras, estaño, oro y diamantes). A estos recursos, se suman las biomineralizaciones con posibilidad de ser fuente
de productos farmacéuticos. El tamaño y valor de dichos recursos son aún poco conocidos pero ofrecen un creciente interés que incentivan la exploración de los fondos oceánicos profundos.

Internal features, mineralogy and geochemistry of Fe-Mn nodules from the Gulf of Cadiz: The role of the Mediterranean Outflow Water

by F. Javier González Sanz

González, F. J., Somoza, L., Lunar, R., Martínez-Frías, J., Martín Rubí, J. A.,  Torres, T., Ortiz, J.E., Díaz del Río, V., 2010. Internal features, mineralogy and geochemistry of Fe-Mn nodules from the Gulf of Cadiz: The role of the Mediterranean Outflow Water. Journal of  Marine Systems 80 (3-4), 203-218.

“High Technology Elements” in Co-Rich Ferromanganese Crusts from the Scotia Sea

by F. Javier González Sanz

González, F. J., Somoza, L., Maldonado, A., Lunar, R., Martínez-Frías, J., Martín-Rubí, J.A., Castillo-Carrión, M., 2010. “High Technology Elements” in Co-Rich Ferromanganese Crusts from the Scotia Sea. Macla 13, 113-114.

Host Rock Volume Change During Alteration Promotes Self-Sealing of Hydrothermal Systems

by Mathijs Booden

Mathijs A. Booden and Jeffrey L. Mauk / SGA Biennial Conference 2011 Extended Abstract

Altered host rocks that surround hydrothermal mineral deposits exchange elements with hydrothermal fluids to produce... more Altered host rocks that surround hydrothermal mineral deposits exchange elements with hydrothermal fluids to produce alteration minerals. The changed mineralogy affects the altered rock’s density and volume and this in turn affects the potential of a hydrothermal reaction to proceed. An increase in rock volume closes fluid pathways and inhibits further reaction, whereas a volume decrease has the opposite effect. In adularia-sericite epithermal deposits, K-metasomatism dominates mass change, where illite and adularia are the principal K-bearing phases. Formation of illite generally decreases host rock volume, whereas proximal adularia formation increases the rock volume. Carbonation may further increase rock volume or offset illite-related volume loss. In orogenic deposits, proximal alteration involves carbonation, sulfidation and sericitization. In each case, proximal net volume effects in appear to be in the order of 5-10% expansion. Therefore, proximal host rock alteration provides a first-order control on hydrothermal fluid flow; host rock alteration leads to volume expansion that promotes sealing of the fault fracture networks that provide the main conduits for hydrothermal flow.

Genetic significance of chromite in Fe-Ni-laterite deposits. Implication from Western Macedonia, Greece

by Charalampos Vasilatos

M. Economou-Eliopoulos, D.G. Eliopoulos, Ch. Vasilatos and M. Soulas, in  in Mineral Exploration and Sustainable Development, 7th Biennial SGA Meeting, Athens, Eliopoulos D.  et al. (eds), Millpress, Rotterdam: 69-72.

Quantifying Metasomatism in Epithermal Au-Ag Deposits: A Case Study From the Waitekauri Area, New Zealand

by Mathijs Booden

M.A. Booden, J. L. Mauk, and M. P. Simpson / Economic Geology / in press

Major element geochemical exploration for epithermal deposits can extend the range of traditional pathfinder elements... more Major element geochemical exploration for epithermal deposits can extend the range of traditional pathfinder elements to a 1-10 km scale, and with knowledge of protolith composition, mass changes associated with hydrothermal alteration can be quantified. In the Hauraki Goldfield of New Zealand, altered andesites and dacites host epithermal Au-Ag deposits and prospects. The major element compositions of equivalent unaltered rocks correlate with whole-rock Zr/TiO2, an immobile element ratio that is preserved during K metasomatism. We used this feature to estimate the initial composition and calculate a mass balance for veinless altered rocks in the Waitekauri area along a 3-km-wide section that extends from the central Waitekauri Fault to the periphery of the alteration zone. The total transferred mass is equal to approximately 11% of rock mass in illite-dominated altered rocks, and 24% of rock mass in adularia-dominated altered rocks. On average mass losses exceed gains. Potassium was gained in most altered rocks, which contain illite and/or adularia as K-bearing hydrothermal minerals. Silica was gained in adularia-quartz-rich rocks close to the Waitekauri Fault. Other major elements are preferentially lost (Ca, Na, Fe, Mg) or effectively immobile (Al, Ti). The greatest K and Si gains occur in adularia-rich rocks that surround Au deposits along the Waitekauri Fault, whereas K gains are progressively lower and Si gains are mostly insignificant in deposits and prospects farther east where illite or interstratified illite-smectite is the dominant K-bearing mineral. In contrast, Na and Ca losses do not increase significantly from the periphery to the core of the Waitekauri area, because losses are commonly complete, and therefore limited by the initial concentration. However, the K and Si gains correlate with other measures of K metasomatism including K/Sr and Rb/Sr values and molar K/(K+Na+2Ca) values, and together these parameters vector from the barren periphery to the orebody-hosting centre of the Waitekauri area. In contrast to major element trends, the pathfinder elements As, Sb and Hg define more local hydrothermal alteration cells within the larger Waitekauri area, some of which surround Au deposits.

Scheelite skarn mineralization associated with the Tinos pluton, Cyclades

by Dimitrios Zouzias

St. Seymour Karen, Tombros Stylianos, Mastrakas Nickolaus, Zouzias Dimitrios, Spry Paul G., Dénès Géorge and Kranidiotis Prokopis (2009): Neues Jahrbuch für Mineralogie - Abhandlungen, Volume 186, Number 1, July 2009 , pp. 37-50(14).

Scheelite (CaWO4) mineralization has developed as disseminations, veinlets and mainly pods within garnet-pyroxene... more Scheelite (CaWO4) mineralization has developed as disseminations, veinlets and mainly pods within garnet-pyroxene skarn and hornfelses in two locations within the contact aureole of a syntectonic calc-alkaline granodiorite to leucogranite pluton on the island of Tinos, Hellas. The pluton was emplaced during a transition from compression (granodiorite) to extension (leucogranite). Opening of conduits assisted by carbofracturing allowed fluid circulation during extension, which resulted in a change of character of contact metamorphism from thermal-isochemical to infiltration metasomatism. During infiltration metasomatism ion exchange involved the plutonic and the country rocks and was intensified by carbofracturing resulting from the pyrometasomatic loss of CO2 from the marbles. Skarn formation may have been initiated due to thermal effects of the pluton with local mass transfer in the host schists and marbles. The Tinos tungsten skarn is an oxidized skarn that retains relics of an earlier less oxidized stage probably mirroring a change in the redox conditions of the leucogranite. Skarn pyroxene is diopside, however, hedenbergite has been preserved locally. Cores of garnet megacrysts from an early skarn formation are rich in grossular component and exhibit sector-zoning, characteristic of growth under contact metamorphic conditions at log fO2 that ranged between −19.8 and −22.9. Garnet overgrowths from a later stage are predominantly andradite and display euhedral crystal boundaries, oscillatory zoning, zonal anisotropy and growth as open space fillings, which are features typical of hydrothermal garnet. Scheelite crystals are enclosed within and display equilibrium boundaries to hydrothermal garnet. They have primary fluid inclusions with an average homogenization temperature Th of 375 °C and salinity of approximately 14 wt% NaCl equivalent. Th of primary fluid inclusions in the coexisting hydrothermal garnet ranges from 310 to 340 °C, of primary inclusions in quartz from quartz-calcite veinlets formed by carbofracturing from approximately 400 to 375 °C and salinity approximately 14 wt% NaCl equivalent. These quartz-calcite veinlets cut mainly the early garnet cores, rich in the grossular component, but rarely the hydrothermal andraditic garnet overgrowths, indicating that scheelite mineralization is associated with the late leucogranitic phase of the Tinos pluton.

Geochemistry of the Serifos pluton (Cycladic islands) and associated iron oxide and sulfide ores: Skarn or metamorphosed exhalite deposits?

by Dimitrios Zouzias

St. Seymour Karen, Zouzias Dimitrios, Tombros Stylianos and Kolaiti Eftyhia (2009): Neues Jahrbuch für Mineralogie - Abhandlungen, Volume 186, Number 3, October 2009 , pp. 249-270(22).

In Serifos island a mid-Miocene pluton was emplaced syntectonically at ca. 11 Ma in a northeasterly trending fault... more In Serifos island a mid-Miocene pluton was emplaced syntectonically at ca. 11 Ma in a northeasterly trending fault zone within schist and marble of the Cycladic Blueschist Unit. The central mass of the pluton consists mainly of hornblende-biotite granodiorite and less tonalite, its border facies is granodiorite to granite. Associated dykes are mainly granodioritic. Amphibole geothermobarometry indicates pluton emplacement at initial maximum P ≈ 3.1 ± 0.6 kbar and T between 748° to 718 °C under hypersolvus conditions. Magnetite-hematite ores, which have been mined since antiquity, occur in the proximity of the Serifos pluton. Most of iron oxide ores are located in marble within the contact metamorphic aureole and have been considered as skarn deposits. However, a few iron oxide and base metal sulfide deposits occur outside the contact aureole. The trace element (V, Ti, Ni) characteristics of the iron ores suggest a sedimentary provenance. The sulfide ores are folded and because the geochemistry of some of the schists of the encasing Blueschist Unit shows them to be of possible metavolcanic origin, on alternative exhalite genesis is suggested for these Serifos ores.