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Correlation Course > Resource Geology > Flashcards

Resource Geology Flashcards

1
Q

Deposits provide more than 50% of the worlds copper from over 100 producing mines.

A

Porphyry copper

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2
Q

Closest relative of porphyry copper deposits

A

Porphyry molybdenum deposit

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3
Q

Sulphide minerals in the porphyry copper system are associated with _____________.

A

hydrothermal alteration of the hostrock intrusion and wallrocks

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4
Q

Stockworks of quartz veinlets, quartz veins, closely spaced fractures and breccias contain ________

A

pyrite and chalcopyrite

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5
Q

________, ________, and _______ occur in large zones of economically bulk mineable mineralization.

A

Molybdenite, bornite, and magnetite

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6
Q

T or F. Most porphyry copper deposits are commonly related to subduction-related magmatism.

A

T

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7
Q

The age of most porphyry copper deposits are of _________ to _________ age

A

Mesozoic and Cenozoic

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8
Q

Porphyry copper deposits have a commonly depositional environment of _______ and ________.

A

oceanic volcanic island and continent-margin arcs

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9
Q

The typical form of porphyry copper deposit are commonly ______ or _______.

A

cylindrical or stock-like

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10
Q

Always present. Characterized by secondary K-spar, biotite and/or chlorite replacing primary K-spar, plagioclase and mafics. Minor sericite may be present.

A

Potassic Zone

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11
Q

Not always present. Characterized by vein quartz, sericite and pyrite and minor chlorite, illite and rutile replacing K-spar and biotite.

A

Phyllic zone

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12
Q

Not always present. Characterized by the clay minerals kaolinite and montmorillonite with minor disseminated pyrite. Plagioclase is strongly altered, K-spar unaffected and biotite chloritized.

A

Argillic zone

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13
Q

Always present. Characterized by chlorite, calcite and minor epidote. Mafic minerals highly altered and plagioclase less so.

A

Porpylitic zone

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14
Q

Coincident with the potassic alteration zone. Generally, several hundred meters in diameter. Relatively LOW SULFIDE CONTENT, but molybdenum is higher than anywhere else in the deposit. Pyrite 2-5% and pyrite/chalcopyrite ratio about 3:1. Mineralization is disseminated rather than stockwork.

A

Inner zone

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15
Q

Lies roughly at the POTASSIC-PHYLLIC BOUNDARY. Pyrite 5-10% and pyrite/chalcopyrite ratio about 2.5:1. Main ore mineral chalcopyrite occurring as stockwork veinlets. Other ore minerals include bornite, enargite and chalcocite.

A

Ore zone

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16
Q

Includes much of the phyllic and argillic (if present) zones. Pyrite quite high (10-15%) and pyrite/chalcopyrite ratio about 15:1. Mineralization both as veins and disseminations. Many additional exotic sulfide phases begin to show up.

A

Pyrite Zone

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17
Q

Coincides with the propylitic zone. Pyrite minor, and copper mineralization rare. Sphalerite and galena common, but usually sub-ore grade. Mineralization approaches true veins.

A

Outer zone

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18
Q

Often major ore carriers in the porphyry system. Have very high grades (2-5% Cu) and can occur both in the porphyry or the country rock. May be formed by hydrothermal activity, gravitational collapse or later explosive volcanism

A

Breccia zone

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19
Q

Predominant sulfide mineral; in some deposits the Fe oxide minerals magnetite, and rarely hematite, are abundant.

A

Pyrite

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20
Q

Chalcopyrite; molybdenite, lesser bornite and rare (primary) chalcocite.

A

Ore minerals

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21
Q

Tetrahedrite/tennantite, enargite and minor gold, electrum and arsenopyrite. In many deposits late veins commonly contain galena and sphalerite in a gangue of quartz, calcite and barite.

A

Subordinate minerals

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22
Q

Both internal between intrusive phases and external with wall rocks; cupolas and the uppermost, bifucating parts of stocks, dikes swarms.

A

Igneous contacts

23
Q

Mainly early formed intrusive and hydrothermal type.

A

Breccias

24
Q

Give rise to ore-grade vein stockworks, notably where there are coincident or intersecting multiple mineralized fracture sets.

A

Zones of intensely developed fracturing

25
Q

Carry chalcocite, covellite and other Cu*2S minerals.

A

Secondary (supergene) zone

26
Q

Marked by ferruginous ‘capping’ with supergene clay minerals, limonite (geothite, hematite, and jarosite) and residual quartz.

A

Oxidized and leached zones

27
Q

T or F. Porpylitic alteration extends upward into the volcano.

A

T

28
Q

T or F. Porphyry deposits are not associated with small, high level stocks ans subaerial calc-alkaline volcanism.

A

F. It is associated

29
Q

There are two types of Porphyry Copper Deposit and which one is hosted by quartz monzonites to grandiorites?

A

Lowell and Guilbert type

30
Q

There are two types of Porphyry Copper Deposit and which one is hosted by quartz diorite and diorite?

A

Diorite type

31
Q

Type of granite that is a product of crustal anatexis.

A

S-type

32
Q

Type of granite that represents the final stage differentiation product of a partial melt generated during plate subduction.

A

I-type

33
Q

What are the following features of calc-alkaline intrusion and volcanic model?

A
  • Caps of advances argillic alteration
  • Diatreme breccia associations
  • Intra-mineral intrusion
  • Vertically elongated porphyry system
  • SCC (sericite, clay, chlorite)
34
Q

Sequence of events associated with emplacement and cooling of a melt at shallow (<2 km depth) crustal levels, as an apophysis to a larger magma source, and the exsolution of magmatic fluids and metals from the upper levels of the porphyry stock.

A

Prograde

35
Q

This stage involves the subsequent cooling of the intrusion, and the porphyry stock and its host rocks become an environment of metal deposition.

A

Retrograde

36
Q

Initial emplacement of melts at shallow crustal levels and the associated cooling and crystallization is accompanied by the formation of zoned alteration assemblages formed in response to the transfer of heat from the melt into the host lithologies.

A

Stage 1: Heat transfer and zoned alteration

37
Q

Dominated by biotite in calc-alkaline magmatic arcs. In areas of crustal rifting involving more silicic intrusions, the potassic alteration is dominated by K-feldspar.

A

Potassic alteration

38
Q

Distal to the central potassic core, reflecting progressively cooler conditions. Secondary amphibole (actinolite) in calc-alkaline environment locally occur with biotite in the outer alteration zone and with epidote in the inner zone.

A

Propylitic alteration

39
Q

Some intrusions, the deep propylitic alteration assemblage is dominated by albite, formed during late stage crystallization of the melt.

A

Albitization

40
Q

Cooling and crystallization of the melt results in the fracturing, especially around the carapace of the intrusion, accompanied by the exsolution of magmatic volatiles. The build up of gas pressure within the cooling magma may initiate fracturing in the brittle host rocks

A

STAGE II: Exsolution of magmatic fluids

41
Q

The most common mineral deposited from calc-alkaline intrusions

A

Quartz

42
Q

The most abundant gangue mineral in the stockwork and sheeted veins

A

Quartz

43
Q

The pre-mineralization gangue minerals can be deposited within the fracture network and result in the formation of a _________.

A

stockwork

44
Q

T or F. This high density of quartz veins implies that a significant quantity of volatiles were released from the melt.

A

T

45
Q

T or F. Fluid inclusion studies indicate that the majority of the stockwork and sheeted quartz veins were deposited from a hot (>300-500ºC), hypersaline (>25-30 wt% NaCl equiv.), two-phase (boiling) brine.

A

T

46
Q

T or F. Fluids which formed the stockwork quartz veins are significantly enriched in quartz.

A

F. Metals

47
Q

Cu-Au mineralization in many porphyry Cu systems post-date Stage I potassic/propylitic alteration, quartz vein formation and advanced argillic alteration, attributed to a progressive change from an environment dominated by magmatic fluids to one dominated by cooler and more dilute meteoric waters.

A

STAGE III: Late stage cooling and mineralization

48
Q

Biotite and K-feldspars form as early Stage II minerals, in thin veinlets w/ quartz, magnetite &/or pyrite and are associated with variable abundances of chalcopyrite.

A

Potassic alteration assemblages

49
Q

Calc-silicate minerals (actinolite, epidote and zeolites occur in fractures and in open spaces replacing wall rock minerals (mainly mafic phases) and post-date the biotite and k-fp.

A

Propylitic alteration assemblages

50
Q

Most Cu-Au mineralization in the SW Pacific is intimately related w/ late chlorite &/or sericite or illitic clay deposition and wall rock alteration. Chlorite dominates at depth and is early, whereas sericite dominates at shallower levels and is late. This zonation is indicative of a progressive decrease in fluid pH at shallower levels.

A

Phyllic alteration assemblages

51
Q

Pervasive quartz-ser-pyrite alteration w/c displays an increasing abundance of chlorite at depth, and post-dates Cu-Au mineralization overprints other alteration assemblages and veins at shallow levels and along the margins.

A

STAGE IV: Post-mineral phyllic, argillic and advanced argillic overprint

52
Q

Derived from a fluid dominated by meteoric water.

A

Sericite

53
Q

Alteration and deposition in open spaces and fractures are inferred to have formed as late hydrothermal alteration minerals

A

Smectite &/or kaolinite ± siderite

Correlation Course (15 decks)

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