Lec 8 - Orthomagmatic deposits

Question 1

Deposits that ofrmfrom coolinga fn crystallization of magma

Answer 1

Magmatic deposit

Question 2

Characteristics of magmatic deposits

Answer 2

1. Occurs near the magma or intrusives
2. Simple mineralogy and products yield are not numerous
3. May occur as strata-like segregationss, as dissemination and as vein-like injection

Question 3

True or False: magmatix textures are mostly the same with parent igneous rock

Answer 3

Trueness

Question 4

The gradationbetween magmatic segregation and hydrothermal activity is manifested by _____________

Answer 4

Wall-rock alteration effect

Question 5

• Igneous rocks defined by mineralogical composition consisting of more than 50% carbonate
• associated with continental rift-related settings
• occurs as small plugs, dikes, sills, veins

Answer 5

Carbonatites

Question 6

Metal concentration in magma

Answer 6

Low degrees of partial melting

Question 7

Most recent carbonatites are found in the _____________

Answer 7

East African Rift

Question 8

Separation of crystallizing minerals based on gravitative differentiation

Answer 8

Magmatic segregation

Question 9

Formed by accumulation of crystals either by floating or settling

Answer 9

Cumulate rocks

Question 10

Titanium deposits

Answer 10

Anorthosite

Question 11

__________ is a lithophile element compatible in both spinel and clinopyroxene relative to ultramafic and mafic melts

Answer 11

Chromite

Question 12

Proterozoic anorthosite massifs: more shallowly derived by partial melting or contaminated by lower continental crust meterials

Answer 12

Ilmenite-rich andesine-typr

Question 13

Proterozoic anorthosite massifs: differentiates of an anorthosite-gabbro magma

Answer 13

Magnetite-ilmenite-rich labradorite-type

Question 14

• Chromite is hosted in ultramafic layered intrusions composed of cumulus crystals
• consists of thin but laterally continuous layers of chromite

Answer 14

Stratiform Chromite Deposit

Question 15

• Pipe-like to pod-like masses of chromite in dunite-harzburgite sequences
• related to ophiolites
• a.k.a. Orogenic-type chromite or alpine-type chromite

Answer 15

Podiform chromite

Question 16

When liquids do not mix

Answer 16

Liquid immiscibility

Question 17

3 kind of liquid immiscibility

Answer 17

• silicate-carbonate
• silicate-oxide
• silicate-sulfide

Question 18

Massive Ni-Cu broadly oayered from mafic to less mafic going upwards

Answer 18

Host intrusions

Question 19

Sudbury Igneous Complex

Answer 19

Ni-Cu magmatic deposit

Question 20

Bvshveld Complex

Answer 20

Stratiform Chromite Deposit

Question 21

A high MgO volcanic flow

Answer 21

Komatiite

Question 22

A texture produced by intergrowth and interpenetration of long, skeletal quench crystals of olivine and pyroxene

Answer 22

Spinifex

Question 23

Repititious oscillation from rock type upward within tye complex. Presumably the repititions represent periodic depletions of critical cations in magma chamber

Answer 23

Rhythmic layering

Question 24

Systematic variation in certain elements within a complex. Indicates differentiation from a single parent magma, as periodic reinjections of new magma would not allow cryptic layering

Answer 24

Cryptic Layering

Question 25

Removal and segregation of mineral precipitates from a melt

Answer 25

Crystal fractionation

Question 26

Formed from the last crystallizing magma enriched in vapor and water pressure - 250-750 degrees celcius - associated with plutonic or regional metamorphism

Answer 26

Pegmatites

Question 27

Formed from one period crystallization: after injection of hydrous siliceous late-stage melt

Answer 27

Zone or Heterogenous Pegmatite

Question 28

Peralkaline igenous complex

Answer 28

Pegmatites

Question 29

- Alkaline, volatile-rich potassic, low density ultrabasic magmas - formed as small degree partial melts of carbonate-bearing and hydrous mantle peridotite - occurs as diatremes

Answer 29

Kimberlites

Question 30

As hot kimberlite magmas >900 C is heated near-surface ground waters, water flashes to steam and results in explosive activity

Answer 30

Diatreme formation

Question 31

Forms in a thick, old, relatively cool “keel” of archean crust

Answer 31

Diamonds

Question 32

1 carat is equal to?

Answer 32

200 mg or 0.2 g

Question 33

Diamonds do not originate in the kimberlite/lamproite, they only provide the transport

Answer 33

Remeber

Question 34

2 TYPE OF DIAMONDS

Answer 34

* P-type derived from peridotite | * E-type derived from eclogite

Question 35

Significant diamondiferous kimberlites occur only in ancient shield regions, including archean cratons and paleoproterozoic mobile belts that border archean cratons, and were themselve underformed since the end of paleoproterozoic era

Answer 35

Clifford’s rule

Question 36

Types of Kimberlites

Answer 36

* Group 1 - recognized world wide, forsterite in serpentinite-carbonate matrix * Group 2- S. Africa, phlogopite in olvine-mica ground mass * Lamproite - australia and India, Ti-phlogopite, Ti-K richterite, olivine, diopside, sanidine