Notable Papers on Porphyry Copper Deposit

Talking about Porphyry Cu Deposits (PCD) will be never ending. In this page, I will talk, describe, and discuss briefly only about the notable books and papers related to PCD, especially in association with Indonesia Region (commonly grouped as Southwestern Pacific Region, including Papua New Guinea, Indonesia, Philippines, and Australia). The books and the papers developed accordance to the development of the sciences, concepts, and approaches. They are strongly influenced by the economic and mining trends.

The following are the papers:

1. Lowell, J.D. and Guilbert, J.M. Lateral and Vertical Alteration-Mineralization Zoning in Porphyry Ore Deposits. 1970.

I am not sure about the first paper about PCD, but this is the “first” paper describing comprehensively the alteration and mineralization of PCD. Evidently, the subject deposit was tilting and diagonally offset into two roughly equalized pieces, and finally eroded. Consequently, the authors reconstructed it to analyze it. The result was the zoning that termed as: potassic, prophylitic,phyllic, and argillic. The terms have been actually adopted from previous literature, which described principal mineral assemblages. It is funny that in the class or course, the lecturer often still showed the alteration model without erasing the San Manuel Fault (Figure 1).

Eventough this model is widely accepted as representative PCD model, however, it cannot be used in all porphyry cases, especially lithocap-overprinted porphyry . Moreover, the alteration mineral assemblages are typically for the related tectonic setting only. We will need to modify them. For example: potassic zones in North Sulawesi and Sumbawa are rarely K-feldspar rich.

Schematic drawing of alteration as the result of structural reconstruction (Lowell & Guilbert, 1970)

 

2. Sillitoe, R.H. Exploration of Porphyry Copper Lithocaps: Pacific Rim Congress, Auckland, 1995. AusIMM, 1995.

Well mineralized (and telescoped) porphyry intrusions may generate at 1-4 km beneath the surface. Thus, they are potentially capped by a large zone of advanced argillic and associated argillic alteration. These are called lithocaps. They may provide a peculiar chemical signatures in the surface.

Thus, the paper summarizes the important characteristic of the lithocaps and the exploration potential for PCD (and supergene Cu enrichment blanket) and the the overlying epithermal deposit. So, the geologists do not need to be dissapointed if the surficial outcrops in the potentially porphyry discovery area are low grades. Perhaps, you are in the lithocaps underlying a big PCD!

 

3. Sillitoe, R.H. Styles of High Sulphidation Gold, Silver, and Copper Mineralisation in Porphyry and Epithermal Environments: Pacrim ’99 Congress, Bali, Indonesia. 1999.

If you, geologist, are assigned by the company to discover PCD but discover high sulphidation epithermal (HSE), then you do not need to worry. HSE is generated in a lithocap environment and definitely correlated to an underlying intrusion, that is probably a PCD (Figure 2), whether economic or not.

HS to Porphyry (Sillitoe, 1999)
Figure 2 – HSE to Porphyry (Sillitoe, 1999)

It is important to define the depth of the formation based on the configuration of the structure, lithology and hydrothermal breccia. Sillitoe subdivided HSE into 3: Deep, Intermediate, and Shallow part. Worldclass HSE deposits are related to Cu-DEEP HSE overprinting a porphyry body (Chuquicamata and Tumpang Pitu – Figure 3) and Au-Ag SHALLOW lithological-control HSE that was subjected to supergene oxidation, thereby permitting a cheap hep-leach (and cyanide leach) processing (Yanacocha and Martabe).

Geology Type Section of Tumpang Pitu, Indonesia
Figure 3 – Geology Type Section of Tumpang Pitu, Indonesia, showing a HSE overprinted porhyry body (Harrison, 2012)

 

4.  Einaudi, M.T., Hedenquist, J.W., and Inan, E.E. Sulfidation State of Fluids in Active and Extinct Hydrothermal System: Transitions from Porphyry to Epithermal Environments. Society of Economic Geologists Special Publication. 2003.

This paper described “the journey” of copper (and iron) minerals as the relative sulphidation state of hydrothermal fluids for various type of magmatic deposits, including porphyries. It presents a compilation of sulphidation states of  of sulfide assemblages in poprhyry and epithermal.

Sulfidation State of Fluids: Porphyry to Epithermal (Einaudi et. al., 2003)

5.  Seedorff, E., Dilles, J.H., Proffett, J.M., Jr., Einaudi, M.T., Zurcher, L., Stavast, W.J.A., Johnson, D.A., and Barton, M.D.Porphyry deposits: Characteristics and origin of hypogene features. 2005

This paper contains a wide range of porphyry types: porphyry Cu, Au, Mo, W, and Sn. It concludes the general characteristic of porphyry, e.g.:

  • Magmatic-hydrothermal process enriching sulfide and oxide ore minerals in veinlets and disseminations in large volumes of rock
  • Occuring within magmatic belts and related to hypabyssal dioritic to granitic intrusion that are porphyrytic and that commonly have an aplitic groundmass.
  • Silica content (SiO2) is intermediate to silicic (>56 wt % SiO2)

This paper describes coherently and more about geochronology or evolution of porphyry genesis, from early, high temperature biotite ± K-feldspar zone (potassic) to muscovite ± chlorite zone (sericitic) to low temperature, clay-bearing zone (advanced argillic  and intermediate argillic). On the other hand, Na plagioclase-actinolite zone (sodic-calcic) and albite-epidote-chlorite-carbonate (prophylitic) commonly lack ore minerals.

What I like most of this paper is graphic below describing relationship of porphyry deposits and the political and economic conditions, metal prices, production, mining and metallurgy technologies, the discovery and the development, industrial trends, scientific approaches, and also the notable papers and books.

Graphical summary of the historical context of porphyry deposits in the 20th century (Seedorf, et.al., 2005)
Graphical summary of the historical context of porphyry deposits in the 20th century (Seedorf, et.al., 2005)

 

6.  Garwin, S., Hall, R., and Watanabe, Y.  Tectonic Setting, Geology, and Gold and Copper Mineralization in Cenozoic Magmatic Arcs of Southeast Asia and the West Pacific. SEG: Economic Geology 100th Anniversary Volume pp. 891-930. 2005.

This paper summarizes the tectonic setting of gold-copper deposit in the SE Asia and Western  Pacific region, and also highlight the relationships between regional tectonic events, subducting slabs, deformation style and the magmatism. Last, it describes the relationship between uplift and exhumation rates for magmatic arcs to the development and preservation of hydrothermal ore deposits. The famous  Robert Hall’s tectonic reconstructions were also displayed in here.

Once I read this paper, I got interested to the map showing the relationship between the distribution of the earthquake hypocenters (forming lineaments) and the deposit positions. In practical, Indonesian geologists like to say it “magic line”, as N 110 E.

Tectonic lineaments are interpreted from topography, gravity, bathymetry, and earthquake hypocenters. They are related to the Au-Cu deposits
Tectonic lineaments are interpreted from topography, gravity, bathymetry, and earthquake hypocenters. They are related to the Au-Cu deposits

 

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 I uploaded and passworded the papers here. Leave your request on the password in the comment box below. 😀

 

 

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