ORE DEP (ULTRAMAFIC TO MAFIC) Flashcards
Deposits related to direct crystallization of magma and usually form in the magma chamber and thus, are deep seated
Magmatic Segragation Deposits
Processes that forms or concentrates ore in a Magmatic Segegration Deposit (3)
1) Gravitative Settling
2) Immiscibility
3) Filter Pressing
A large sill like body of igneous rocks which exhibit VERTICAL LAYERING or difference in COMPOSITION OR TEXTURE which may cover an area from 100 sq.km to 50,000 sq.km. and several hundred to over a kilometer thickness
Layered Mafic Intrusion
What is the average age of the World’s LMIs?
Proterozoic
In which landforms do LMIs usually occur?
Stable platform as Intrusion
What is the average composition of LMIs?
Gabbro
How many LMIs are known in the world?
8
How many LMIs have deposits of Cr?
3 of which two are mined from chromium
1) Bushveld , SA
2) Great Dyke, Zimbabwe
Only LMI mined for Platinum?
Bushveld
Largest Cr Resourve accounting to 70% of the world’s
Largest PGE Resource
Bushveld Igneous Complex
In what part of the Busveld Complex are rich in PGEwith Chromite?
Merensky Reef and UG2
what type of intrusion is the BIC?
Lopolith
Main Chromitite Seam in BIC?
Steelport Main Chromite Seam (UC1)
Chromite in Anorthosite deposit?
UG1
Largest Ni Resource said to be derived due to complete melting of continental crust due to meteorite impact
Sudbury Crater, Canada
Percentage of Intermediate to Calcic Plag
90%
Age of most anorthosite
Proterozoic
Two types of Anorthosite hosted - Ti
1) LMI fromed by gravitational settling mostly composed of Anorthite
2) Proterozoic Massif or plutons containg andesine to Labradorite (An 35-65)
Titaniferous ores in Anorthsoites
Ilmenite - FeTiO3
Rutile TiO2
IN what type of magma is an Fe-Ti oxide liquid a residue?
Mafic Magma Differentiation
Two Types of Proterozoic Anothoside
1) Ilmenite Rich -Andesine Types
2) Magnetite-Ilmenite Rich - Labradorite Typr
One of the two types, SHALLOWLY derived by partial melting or contaminated by LOWER Continental Crust Material
Andesine Type (Ilmenite Rich)
Example of Ilmenite rich Anorthosite which is also the largest deposit of Ti in the World
Lac Tio, Quebec, Canada
Forms by differentiaion of an anorthosite-gabbro magma
Labradorite Type (Magnetite-Ilmeite Rich)
Volatile CO2 Rich
K-Ultramafic rock
Related toPhreatomagmatic Breccia Pipe or Igneous Dike (Diatreme)
dominated by OLIVINE with subordinate mienrals of Mantle Origin
Kimberlites
Ca Olivine
Monticellite
Potassic Rich Mg-Lamprophyres
Lamproites
Age of Productive Kimberlites
80-100 Ma
250 Ma
1000 -1100 Ma
Most productive Kimberlites?
Mesozoic
Alteration of diamonds in which the microstructure of some carbon and low alloy steels break down after long exposure to elevated temperatures causing material to weaken and be susceptible to cracking failures
Graphitization
partial or complete remelting or dissolution of a mineral by magma resulting from change in P,T or Composition
Resorption
Major Producers of diamon in the later 1980s
1) South Africa
2) Zaire
3) Russia
Majority of Diamond (90%) deposits are derived from?
Placer deposits
represent a rapdi, violent upward rush of deep mantle material from the asthenosphere 200 kms below the surface in the form of a diatreme with explosive surface expression
Geological Boreholes (Kimberlites)
Methos of Diamond Extraction or recovery which uses ferosilicon in which diamong adhere to greased surface
Haevy Liquid Seperation
A method in which a jet of air activated by photocells that perceive visible light flrouresence is emitted in diamond by an x-ray beam as concentrates move along a V belt the air jet popping diamonds and adjacent particles off
Sortex Method
Cylindrical Pipelike bodies of Calcite, Dolomite and/or Sierite which are concentrcally znes w
Carbonatites
What are the ages of Such deposits?
E.Proterozoic to Recent
Two types of Carbonatite
1) Magnetite Apatite Rich - Palabroa
2) REE-Fl-Ba-Rich - Mountain Pass, USA
Complex consising of micacaeous pyroxenite, a diopside-phlogopite rock containing 15% Apaatite
Palabora South Africa
Which of the three types are most economocically important
Central Pipe (Loolekop)
Deposits mined in Carbonatites?
Copper and Phosphate
Type of Carbonatites in which Cu occur as chalcopyrite veinlets, low P-Ti-Fe
Transgressive Carbonatite
Carbonatite in which Cu is mainly in Bornite dissemination, low P-Ti-Fe
Banded Carbonatite
Type of carbonatite in which Cu occurs as Bornite Disseminations w/ minor Chalcopyrite high P-Ti-Fe
Forkstorite
