Alteraciones Hidrotermales

UNIVERSIDAD CENTRAL DEL ECUADOR FACULTAD DE INGENIERÍA EN GEOLOGÍA, MINAS, PETRÓLEOS, AMBIENTAL ESCUELA DE GEOLOGIA YACIMIENTOS MINERALES NOMBRE: RICARDO VEGA FECHA: 10/12/2018 Tema: Principales alteraciones hidrotermales: describir rangos de temperatura de formación, paragénesis mineralógica, en que yacimientos es frecuente, relación entre estas alteraciones y conclusiones. ALTERACIÓN SILICIFICACIÓN

RANGO wide range of T0.

SAUCERITIZACIÓN

2500

POTÁSICA

6000 - 4500

SERICITIZACIÓN

(T0)

ALTERACIONES HIDROTERMALES PARAGÉNESIS YACIMIENTOS Development of secondary quartz, jasper, It is associated with the chalcedony, chert, opal or other siliceous deposition of sulfides mainly. varieties in the box rocks of epigenic deposits. Epidote (or zoisite or clinozoisite) + chlorite Porphyry Cu, high sulphidation + albite carbonate ± sericite ± epithermal, montmorillonite ± low-sulphidation epithermal, geothermal septachlorite ± apatite ± anhydrite ± ankerite ± hematite ± pyrite ± chalcopyrite K-feldspar (orthoclase) + biotite + quartz ± Porphyry Cu magnetite ± sericite (or muscovite) ± albite ± chlorite ± anhydrite ± apatite ± rutile ± epidote ± chalcopyrite ± bornite ± Pyrite Sericite + quartz + pyrite ± biotite ± chlorite Porphyry Cu ± rutile ± leucoxene ± chalcopyrite ± illite

RELACIÓN ENTE ALTERACIONES Addition of silica, alkali leaching, aluminum leaching Associated with propylitic alteration.

Potassic alteration is usually accompanied by sulphides (chalcopyrite, pyrite, molybdenite). This alteration grades into the potassic type by increasing amounts of K-feldspar

ARGILITICA AVANZADA

4000-5000

Pyrophyllite + kaolinite (or dickite) ± quartz ± sericite ± andalusite ± diaspore ± alunite ± topaz ± zunyite ± enargite ± tourmaline ± pyrite ± chalcopyrite ± hematite

Porphyry Cu, high- sulphidation Epithermal, geothermal

PROPILITIZACIÓN

2200-3400

Chlorite, epidote, actinolite and tremolite

ARGILITIZACIÓN INTERMEDIA

3000

Chlorite + sericite ± kaolinite ± montmorillonite ± illite-smectite ± calcite ± epidote ± biotite ± pyrite

Porphyry Cu, high sulphidation epithermal, low-sulphidation epithermal, geothermal Porphyry Cu, highsulphidation epithermal

CLORITIZACIÓN

Low T0

ZEOLITIZACIÓN

Low T0

Replacement of ferromagnesian minerals with chlorite. Estilbita, natrolita, heulandita

CARBONITIZACIÓN

Average T0

Calcite, ankerite and dolomite

ALUNITIZACIÓN

500 - 3000

Alunite and quartz as a result of feldspar alteration

SERPENTINIZACIÓ N SKARNIFICACIÓN

3000

Serpentine, brucite, and magnetite

High (contact metamorphis m) Minor

Limestone Garnets (andradite and grosularia), wollastonite, epidote, diopside (Px), idocrase, (chlorite, actinolite.

Deposits associated with sulfides. Deposits of native copper in amygdaloid basalts Carbonate alteration can form zonal patterns around ore deposits with more iron-rich types occurring proximal to the deposit. Alunitic alteration is closely associated with certain hot springs environments. Submarine environments, gold and nickel deposits Cu porphyries, reduced skarn (Au, W and, Sin), metasomatic replacement of dolomitic limestones (rich in Mg).

and/or biotite, and into the argillic type by increasing amounts of clay minerals. Alunitic alteration is part of advanced argillic alteration, and in the presence of abundant sulphate ions and Al-rich protoliths may become a dominant phase. In some situations, there can be intense albitisation, chloritisation or carbonitisation Zoning within the intermediate argillic alteration may be present with kaolinite being closer to the phyllic zone, whereas montmorillonite clays occur in the outer zones. This alteration is related to propilitization. Related to propylitic alteration Particularly common in limestones (dolomitized) and in basic rocks (ankeritization) This alteration can be hypogenic or supergenic. Serpentinization can occur in ultrabasic rocks also by deuteric action. This alteration can be essentially isochemical with removal of CO2 and other times it includes the introduction of

metasomatis m ALBITIZACIÓN

High T0

Dolomites fosterita (olivine), serpentinite, talc, tremolite, chlorite. Aluminous material becomes albite or oligoclase sodium

silica, Mg, Fe and volatiles (F, Cl, B and H2O), with an extensive loss of CO2. In porphyritic systems it is interpreted as an early and profound alteration during late stages of crystallization of a magma.

Normally associated with high temperature propylitic alteration

Conclusiones: • • • • • •

Procesos de alteración particularmente en sistemas de pórfido. Los efectos de la alteración hidrotermal y la mineralización se extienden en un gran volumen de rocas alrededor de la pared y por encima de los intrusivos. La alteración potásica es especialmente común e importante en pórfidos y Sistemas de mineralización epitermal, donde se produce en el núcleo de alta temperatura. En la alteración propilitica en algunas situaciones, puede haber una intensa albitización, clorización o carbonización. Los procesos que conducen a la alteración en los sistemas de pórfido son: adición volátil, (alteración propilítica), hidrólisis (sericítica, argílica avanzada e intermedia), argílico), intercambio alcalino (alteración potásica, sódica-cálcica) y adición de sílice. Los tipos de alteraciones hidrotérmal argilitica avanzadas, potásicas, propilíticas, sericiticas, se aplican a la mayoría de los depósitos hidrotermales, y el sistema de mineral de pórfido-epitermal. La composición de las rocas de la pared puede desempeñar un papel importante en la determinación del tipo de conjuntos minerales.

Referencias 1. Pirajno F. Hydrothermal Processes and Mineral Systems. primera ed. Science S, editor. Australia: Geological Survey of Western Australia, Perth, WA, Australia; 2009.