PORPHYRY COPPER ALTERATION

Howell

Figure 1A: Schematic illustration of alteration zoning and overprinting relationships in a calc-alkalic porphyry system. Mineralization occurs in potassically altered intrusions and adjacent wallrocks. Three propylitic alteration subfacies (actinolite, epidote and chlorite zones) can occur around the potassic-altered rocks. In this example, the porphyry has been partially overprinted by a lithocap (silicic and advanced argillic alteration assemblages) that contains a domain of high sulfidation epithermal mineralization. The roots of the lithocap can produce a pyrite halo to the porphyry system. The degree of superposition of the lithocap into the porphyry system is contingent on uplift and erosion rates at the time of mineralization. B: Schematic illustration of alteration zoning and overprinting relationships in an alkalic porphyry system, based on geological relationships from the Cadia East porphyry Cu-Au deposit (Tedder et al., 2001; Wilson 2003; Cooke et al., 2007). The alkalic equivalent of a lithocap contains less acidic alteration assemblages (albite – sericite – K-feldspar). The propylitic sub-facies are more complicated than in the calc-alkalic example, and calcium-bearing alteration minerals (calcite, actinolite, epidote, garnet) occur in the core of the deposit, in contrast to calc-alkalic porphyries. Inspirations for this diagram came from Sillitoe and Thompson (2006). Abbreviations: ab – albite; act – actinolite; anh – anhydrite; Au- gold; bi – biotite; bn – bornite; cb – carbonate; chl – chlorite; cp – chalcopyrite; epi – epidote; gt – garnet; hm – hematite; Kf – K-feldspar; lm – laumontite; mt – magnetite; pr – prehnite; py – pyrite; qz – quartz; ser – sericite; tm – tourmaline. Proceedings of Exploration 07: Fifth Decennial International Conference on Mineral Exploration" edited by B. Milkereit, 2007, p. 791-809 Advances in Geological Models and Exploration Methods for Copper ± Gold Porphyry Deposits Holliday, J. R. [1], Cooke, D. R. [2]

Schematic diagram of generalized alteration zones within porphyry copper systems. (Sillitoe, 2010).

Agus, 2011

MORENCI, AZ

PORPHYRY COPPER ALTERATION ALTERATION ZONES BY ROCK TYPE INTRUSIONS CENTRAL CORE = K-SILICATE ZONE - POTASSIC BIOTITE +/- K-SPAR INTERMEDIATE – “SERICITE” ZONE - PHYLLIC QUARTZ + CHLORITE OVERPRINXXTED BY “SERICITE” + PYRITE WALL ROCKS - FURTHER FROM INTRUSION PROPHYLITIC ZONE EPIDOTE, CHLORITE, ALBITE LEACHED CAP ADVANCED ARGILLIC ALTERATION PRODUCT OF ACID WATER LEACH FORMED BY ABSORPTION OF MAGNETIC VAPOR INTO METEORIC WATER

ALTERATION MINERALS PORPHYRY COPPER EPIDOTE, CARBONATES, ZEOLITES DICKITE, KAOLINITE, ILLITE, SMECTITE, MUSCOVITE ALUNITE, JAROSITE, GYPSUM, ANHYDRITE CHLORITE, BIOTITE, PHLOGOPITE, TOURMALINE PYROPHYLLITE, DIASPORE, ZUNYITE, TOPAZ SELECTED COPPER BEARING

ARGILLIC  ADVANCED ARGILLIC PROPYLITIC CHLORITE, EPIDOTE, ZEOLITES MONTMORILLONITE, ILLITE, CARBONATE POTASSIC FELDSPARS, BIOTITE, PHLOGOPITE, CHLORITE, TOURMALINE PHYLLIC MUSCOVITE ILLITE, KAOLINITE, QUARTZ ARGILLIC  ADVANCED ARGILLIC TOPAZ, ZUNYITE, PYROPHYLLITE, DICKITE, DIASPORE, KAOLINITE, ILLITE, ALUNITE LEACHED CAP ENVIRONMENT ALUNITE, KAOLINTE, ILLITE, DIASPORE, IRON OXIDES CAPPER SULFATES, HYDROXIDES. HALLOYSITE

PROPYLITIC ALTERATION Forms the outermost alteration zone at intermedite to deep levels in the porphyry system. It can be mineralogically zoned from inner actinolite-rich to outer epidote rich facies. chlorite, epidote, albite, calcite, actinolite, illite, clay pyrite

PORPHYRY COPPER - PROPYLITIC ZONE MINERALS DOMINANT ACCESSORY SECODARY ALTERATION ALBITE ACTINOLITE* CHLORITE* CALCITE* BIOTITE*(SECONDARY) HYDROUS BIOTITE CHLORITE HEMATITE SERICITE EPIDOTE ZEOLITES* SMECTITE* QUARTZ* VERMICULITE* *INFRARED ACTIVE MINERALS

PROPYLITIC ALTERATION includes; Fe- chlorite, Mg-chlorite, epidote, actinolite, calcite, illite, montmorillonite, albite, pyrite. PROPYLITIC PROPYLITIC

BIOTITE RICH ALTERATION (Thompson and Thompson, 1996) POTASSIC ZONE BIOTITE RICH ALTERATION (Thompson and Thompson, 1996) This alteration type is found in the core of porphyry deposits. It may form large peripheral alteration zone in wall rocks (without K-spar) and zones out to propylitic alteration. Minerals include biotite, phlogopite, K-spar, magnetite, quartz, anhydrite, albite-sodic plagioclase, actinolite, rutile, apatite, “sericite”, chlorite, and epidote.

POTASSIC POTASSIC - Potassic alteration shows Actinolite, biotite, phlogopite, epidote, iron-chlorite, Mg-chlorite, muscovite, quartz, anhydrite, magnetite. Potassic - K-silicate alteration includes "albite", anhydrite, quartz, muscovite and epidote.

SODIC, SODIC-CALCIC Occurs with minor mineralization in the deeper parts of some porphyry systems. and is a host to mineralization in porphyry deposits associated with alkaline intrusions. albite, actinolite, diopside, quartz, magnetite, titanite, chlorite, epidote , scapolite

SODIC – CALCIC ALTERATION Albite, actinolite, Fe-chlorite, epidote, Mg-chlorite, marialite, mizzonite, diopside, quartz, magnetite

PHYLLIC ALTERATION Phyllic alteration commonly forms a peripheral halo around the core of porphyry deposits. It may overprint earlier potassic alteration and may host substantial mineralization. Detectable minerals include muscovite, illite, quartz, pyrite, chlorite, hematite, and anhydrite.

PORPHYRY COPPER - PHYLLIC ZONE MINERALS DOMINANT ACCESSORY SECODARY ALTERATION QUARTZ CHALCOPYRITE PYRITE MOLYBDENITE KAOLINITE* “SERICITE”/ILLITE* TOURMALINE* “SERICITE”/MUSCOVITE* *INFRARED ACTIVE MINERALS

Phyllic alteration includes: Illite, muscovite, iron chlorite, Mg-chlorite, gypsum, anhydrite, quartz, pyrite.

STOCKWORKS TOMBSTONE, AZ

PHYLLIC TOURMALINE

TOURMALINE MINERALS ALTERATION DEPOSIT TYPE Tour, Sericite PHYLLIC INTRUSION – PC Found in Phyllic zone Pyrophyllite, Qtz AA INTRUSION-PC upper parts of PC Sericite, Andal, Dia pyrite vein envelopes Alun, topaz, Tour, dumo Pyrite, Hem Tour, Pyr, Chalco MINERALIZED PC as cement in mineralized BXA Topaz, Muscovite, Greisen INTRUSION high Temp Alt – peraluminous Qtz, tourmaline granites –related mineralztn Tour, Muscovite, Qtz TOURMALINE SMS pervasive replacement below massive sulfide; Assoc w/ abundant dissem sulfides limited to feldspathic strata.

INTERMEDIATE ARGILLIC Intermediate argillic alteration generally forms a structurally controlled to widespread overprint on other types of alteration in many porphyry systems. The detectable minerals include illite, muscovite, dickite, kaolinite, Fe-chlorite, Mg-chlorite, epidote, montmorillonite, calcite, and pyrite.

PORPHYRY COPPER - INTERMEDIATE ARGILLIC MINERALS DONINANT ACCESSORY CHLORITE* CHALCOPYRITE ILLITE* GOLD ILLITE/SMECTITE* HEMATITE KAOLINITE* MAGNETITE QUARTZ* PYRITE SMECTITE* *INFRARED ACTIVE MINERALS

INTERMEDIATE ARGILLIC alteration contains muscovite, illite, chlorite, kaolinite, dickite, montmorillonite, calcite, epidote, pyrite.

ADVANCED ARGILLIC This is an intense alteration phase, often in the upper part of porphyry systems. It can also form envelopes around pyrite-rich veins that cross cut other alteration types. The minerals associated with this type are higher temperature and include pyrophyllite, quartz, andalusite, diaspore, corundum, alunite, topaz, tourmaline, dumortierite, pyrite, and hematite.

PORPHYRY COPPER - ADVANCED ARGILLIC MINERALS DONINANT ACCESSORY ALUNITE* CHALCEDONIC QUARTZ* DICKITE* DISPORE* KAOLINITE* GOETHITE PYROPHYLLITE* JAROSITE* QUARTZ* *INFRARED ACTIVE MINERALS

ADVANCED ARGILLIC higher temperature minerals Topaz, pyrophyllite, andalusite, dumortierite, tourmaline, alunite, diaspore, quartz, hematite pyrite.

SUPERGENE Secondary (supergene) zones carry chalcocite, covellite and other Cu2S minerals (digenite, djurleite, etc.), chrysocolla, native copper and copper oxide, carbonate and sulphate minerals. Oxidized and leached zones at surface are marked by ferruginous “cappings” with supergene clay minerals, limonite (goethite, hematite and jarosite) and residual quartz.. Panteleyev, A. (1995): Minerals include: antlerite, bisbeeite, brochantite, chalcoalumite, claringbullite, conichalcite, crednerite, cuprite, delafossite, graemite, nantokite, paramelaconite, paratacamite, rosasite and spangolite, aurichalcite, connellite, cyanotrichite, malachite and shattuckite are additional supergene copper.

COPPER CARBONATES porphyry systems can include Azurite Malachite Aurichalcite Rosasite

CU phosphates include libelhenite, pseudomalachite, and turquoise. Cu chlorides include atacamite, connellite, and cumengite

Cu-ARSENATES bayldonite, chenevixite conichalcite, clinoclase olivenite.

Cu-SILICATES chrysocolla, dioptase, Papagoite shattuckite

Cu-SULFATES antlerite, brochantite, chalcanthite, cyanotrichite, kroehnite, spangolite

LEACHED CAP Minerals in the leached cap environment include alunite, kaolinite, illite, diaspore, iron oxides, copper sulfates, and copper hydroxides. AND HALLOYSITE

LEACH CAP MINERALS goethite, hematite, jarosite, kaolinite, chrysocolla, antlerite, brochantite, diaspore, turquoise. alunite.

Other leach cap copper bearing atacamite, azurite, malachite, chrysocolla, kaolinite.

Exotic copper mineralization is a complex hydrochemical process linking supergene enrichment, lateral copper transport, and precipitation of copper oxide minerals in the drainage network of a porphyry copper deposit.

POTASSIC ZONE ALTERATION MINERALS

MORE POTASSIC ZONE

PORPHYRY COPPER ALTERATION MINERALS

COPPER BEARING ALTERATION MINERALS