Resource Geology

Question 1

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

Answer 1

Porphyry copper

Question 2

Closest relative of porphyry copper deposits

Answer 2

Porphyry molybdenum deposit

Question 3

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

Answer 3

hydrothermal alteration of the hostrock intrusion and wallrocks

Question 4

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

Answer 4

pyrite and chalcopyrite

Question 5

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

Answer 5

Molybdenite, bornite, and magnetite

Question 6

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

Answer 6

T

Question 7

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

Answer 7

Mesozoic and Cenozoic

Question 8

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

Answer 8

oceanic volcanic island and continent-margin arcs

Question 9

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

Answer 9

cylindrical or stock-like

Question 10

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

Answer 10

Potassic Zone

Question 11

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

Answer 11

Phyllic zone

Question 12

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.

Answer 12

Argillic zone

Question 13

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

Answer 13

Porpylitic zone

Question 14

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.

Answer 14

Inner zone

Question 15

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.

Answer 15

Ore zone

Question 16

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.

Answer 16

Pyrite Zone

Question 17

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

Answer 17

Outer zone

Question 18

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

Answer 18

Breccia zone

Question 19

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

Answer 19

Pyrite

Question 20

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

Answer 20

Ore minerals

Question 21

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.

Answer 21

Subordinate minerals

Question 22

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

Answer 22

Igneous contacts

Question 23

Mainly early formed intrusive and hydrothermal type.

Answer 23

Breccias

Question 24

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

Answer 24

Zones of intensely developed fracturing

Question 25

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

Answer 25

Secondary (supergene) zone

Question 26

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

Answer 26

Oxidized and leached zones

Question 27

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

Answer 27

T

Question 28

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

Answer 28

F. It is associated

Question 29

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

Answer 29

Lowell and Guilbert type

Question 30

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

Answer 30

Diorite type

Question 31

Type of granite that is a product of crustal anatexis.

Answer 31

S-type

Question 32

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

Answer 32

I-type

Question 33

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

Answer 33

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

Question 34

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.

Answer 34

Prograde

Question 35

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

Answer 35

Retrograde

Question 36

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.

Answer 36

Stage 1: Heat transfer and zoned alteration

Question 37

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.

Answer 37

Potassic alteration

Question 38

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.

Answer 38

Propylitic alteration

Question 39

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

Answer 39

Albitization

Question 40

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

Answer 40

STAGE II: Exsolution of magmatic fluids

Question 41

The most common mineral deposited from calc-alkaline intrusions

Answer 41

Quartz

Question 42

The most abundant gangue mineral in the stockwork and sheeted veins

Answer 42

Quartz

Question 43

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

Answer 43

stockwork

Question 44

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

Answer 44

T

Question 45

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.

Answer 45

T

Question 46

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

Answer 46

F. Metals

Question 47

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.

Answer 47

STAGE III: Late stage cooling and mineralization

Question 48

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.

Answer 48

Potassic alteration assemblages

Question 49

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.

Answer 49

Propylitic alteration assemblages

Question 50

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.

Answer 50

Phyllic alteration assemblages

Question 51

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.

Answer 51

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

Question 52

Derived from a fluid dominated by meteoric water.

Answer 52

Sericite

Question 53

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

Answer 53

Smectite &/or kaolinite ± siderite