Exploration of minerals

Question 1

Concentration factor equation

Answer 1

Grade (%) ÷ average crystal abundance (%)

Question 2

What is the main ore mineral for copper??

Answer 2

Chalcopyrite CuFes2

Question 3

what is secondary enrichment??

Answer 3

when metal ore is leeched from within surface rocks and precipitate just below WT

Question 4

Formation of chalcopyrite

Answer 4

hydrothermal fluids dissolve copper from I rocks
precipitate in surrounding contact met sed rocks
often found in hydrothermal veins

Question 5

Why don’t we exploit copper from chalcopyrite

Answer 5

Conc factor not high enough
not at cut off grade
part of resource not reserve
inaccessible

Question 6

Flow diagram for secondary enrichment
(of chalcopyrite)

Answer 6

Chalcopyrite

In forms of sulphides - insoluble in H20

Chalcopyrite exposed and chem weathering /oxidation

produces copper sulphate

this is soluble in H20

percolates down in ground

reaches WT = saturated and anaerobic

reduced + dep as Cu just below WT

now much more conc and econ viable to mine

Question 7

What is gossan?

Answer 7

an insoluble cap of iron oxide at the surface of a mineral vein

Question 8

why are gossans useful

Answer 8

marker for Cu below surface left over from secondary enrichment of chalcopyrite

Question 9

porphyry def

Answer 9

a large igneous intrusion with a porphyritic texture (2 stage cooling)

Question 10

formation of porphyry cooper dep

flow diagram

Answer 10

form as a result of hydrothermal processes associated with granite intrusions at convergent plate margins

C plate boundary

melting

granite intrusion (S and wet) high H20

M chamber cools and common S minerals form e.g. quartz and feldspar

Leftover= H2O and incompetent metals e.g. Au Cu U Mo called at top of M chamber

some crystals take up more space as solid rather than liquid

less space pressure builds

surrounding C rock fractures

hydrothermal fluid moves away from porphyry and cools

metals are dep /come out of solution along fractures as come out of solution at diff temps

form mineral veins

Question 11

What is a Placer deposit

Answer 11

surface deposits formed by sed processes of weathering and erosion, transport and dep

Question 12

why are Placer dep important

Answer 12

Dense physically and chem resistant mineral e.g. cassiterite , gold and diamond can be converted by these processes until small but high grade ore dep

Question 13

How do Placer deps form?

Answer 13

weathering
ore is broken up by mech/
left as insoluble metals by chem

ore and gangue sep into individual grains

weather metals transported by H20 in river + sea (sorted by grain size hardness and density)

when velocity slows preferentially dep as ore mix with unconsolidated sand and gravel

become conc as resistant to erosion and being dissolved

all mins have sim properties: hard + little cleavage, unreactive so don’t dissolve,dense- dep first

Question 14

5 places placer deposits form

Answer 14

Meander bends

plunge pools

upstream projections

downstream confluences

on beaches

Question 15

How do placers form on meandering bends?

Answer 15

current swings around outside bend

velocity higher on outside
lower inside

results in dep on inside (placer dep) and erosion on outside

Question 16

how do placer deps form in plunge pools

Answer 16

river flows erodes less resistant rock creating waterfall

turbulent water and boulder at bottom of waterfall scour out deep hollow

plunge pool

dense placer min trapped in sed in plunge pool

Question 17

how do placer deps form at upstream projections

Answer 17

projections e.g. Dykes in river bed will trap dense placer mineral

on upstream side

may be where hard rock projects out or just small scale like ripples

Question 18

how do placers form downstream of confluences

Answer 18

fast flowing tributary joins slower flow river

current drops

dense placer min dep into mid channel sandbar

Question 19

how do placers form on beaches

Answer 19

river transport sed to sea

sed move along coast by longshore drift

waves throw sediment up to beach via swash

energy drops in wave during backwash - dense placer minerals deposited

Question 20

4 geophysical techniques for exploration of minerals

Answer 20

Gravity surveys

magnetic surveys

electromagnetic surveys

electrical resistivity survey

Question 21

Gravity surveys

Answer 21

gravimeter - measures variations in grav field strengths

shows varied results from rocks and mins

plotted with lines showing equal strengths

+= high density metal ore/ M or UM intrusion

-= low density S intrusion e.g. hydrothermal vein or oil + gas or aquifer

Question 22

magnetic survey

Answer 22

magnetometer measures variation in mag field strength

+= rich in Mg and Fe
due to M or UM intrusion (may contain cumulate ore dep)
or presence of haematite, magnetite or pyrite

Question 23

electromagnetic survey

Answer 23

measures ground conductivity using electromagnetic inductor

give value as % of secondary relative field: primary field

electricity produced by transmitted induced current in conductive minerals e.g. metal ore

good for metal sulphide minerals e.g. chalcopyrite

use very low frequency

Question 24

electrical resistivity survey

Answer 24

2 electrodes placed in ground

pass e current between

if underlying rock good conductor = low res

metals = good conductors so lower res

used for gold exploration

Question 25

4 geochemical techniques for exploration of minerals

Answer 25

sediment stream sampling soil sampling water sampling vegetation sampling

Question 26

stream sediment sampling

Answer 26

1 to 2 kg collected from beds and analysed for mins of interest interpretation based on: downstream of source will have anomalous metal values upstream of source = normal size of anomaly decreases downstream due to dilution by surface water run off + sed entering river catastrophic dilution- occurs where tribs meet best- sample each trib directly upstream of confluence p- anomaly tracked backward upstream to source

Question 27

soil sampling

Answer 27

used for local follow ups in target area with lack of outcrop handheld tools used to collect soil + subsoil sample using systematic grid pattern interpretation depends on: soil samples on top of and downstream of source will me anomalous upslope=normal

Question 28

what further exploration occurs post geochem and physical surveys?

Answer 28

promising areas are mapped, may collect min and rock samples have location and potential grade GIS used to view and analyse quantitive spatial relationship (creating map from data from surveys) to target selection then maybe borehole to narrow down ares and test may test in lower value ores

Question 29

purpose of exploration drilling

Answer 29

provides most accurate info - expensive diff drills used e.g. diamond for core samples down hole logging- make borehole large enough for device more geophys surveys aims to detect: useful/not ore, how much ore present, grade, how much gangue is present, depth and extent of ore body and how it can be used

Question 30

reserve defenition

Answer 30

metal that can be extracted with todays technology and is economically viable

Question 31

why is estimating reserves important and what must we know to estimate

Answer 31

help eval deposit is the reserve probable makes allowances for waste rock that dilute ore or unavoidable losses only way to find out if min is profitable to mine it as if not no longer a reserve

Question 32

kriging method

Answer 32

used in mining to determine size and location of valuable resource based in comp programs using stats and projections feed data into program (what and where) use know data from prev sites produce 3D block image of valuable material and grade not necessarily correct but improves with each use-machine learning uses geostats

Question 33

how are block models of ore body made and why are they useful

Answer 33

made by computer program e.g. kriging instead of drilling anywhere only drill into blocks with highest grade so cheaper reduces losses and expensive as dont have to mine everywhere

Question 34

other considerations when determining viability of resource extraction

Answer 34

geological operational economic

Question 35

geological considerations for viability

Answer 35

geological setting whether areas of V high grade style and zonation of mineralisation e.g sharp or gradual boundaries how easy rock is to work into presence of toxic elements

Question 36

operational consideration for viability of resource

Answer 36

type of mine and stability e.g. open pit or underground method, rate of extraction and processing pollution management and acid mine drainage dilution of waste rock mixed with ore water content, drainage and pumping

Question 37

economic consideration for viability of resource

Answer 37

set up cost- plant assembly level of cut off grade long term projections for metal price of ore closure and reclamation plans as laid out in planning consent

Question 38

factors effecting accuracy of est of reserve

Answer 38

variation in grade and size of ore body unexpected geo conditions e.g. faulting variations in economic climate and demand improvement in extraction tech

Question 39

life cycle of mine

Answer 39

stage 1- design and planning stage 2- construction stage 3- production stage 4- processing stage 5- rehabilitation and reclamation

Question 40

design and planning of mine

Answer 40

assumes surveys done and assess grade + low cost processing profit remitted- more likely to succeed if needs of locals are met as benefits shared rehab and reclamation are part of planning

Question 41

construction of mine (what do they build?)

Answer 41

extraction and processing facilities and roads and enviro management systems and housing / other facilities

Question 42

production in mine

Answer 42

may be open pit or underground depends on depth and size of target body and limits imposed by health and safety as well as tech, enviro damage and economics

Question 43

processing in mine

Answer 43

mineral materials sent through huge crushers or mills to sep commercially valuable from gangue/waste rock means transport to smelter is more economic

Question 44

rehabilitation and reclamation

Answer 44

once exhausted site is dismantled and land is returned to og state large open pit mine may mean this is impossible aim is to insure public health and safety and minimise enviro impact by removing waste, hazardous material, preserving water quality, stabilise against erosion and establish new veg

Question 45

types of mines

Answer 45

open pit/cast mine stope mining longwall retreat mining

Question 46

open cast/pit mining SEE BOOKLET FOR DIAGRAM

Answer 46

for ore close to surface often more economical to strip away overlying by quarrying than building underground mine

Question 47

open pit mining pros and cons

Answer 47

pros- cheaper than underground V efficient and high r of production only small workforce safter no vent equip required cons- V bad for enviro slope stability problems of central mounds lower grade ore

Question 48

stope mining SEE BOOKLET FOR DIAGRAM

Answer 48

most productive to extract ore from ore body itself without need to construct additional shafts exact methods depend on size and grade lowers cavity drills shafts straight down and then horizontal levels into ore body (usually have supports and may be back filled ) blast - break - fracture - extract - this is stoping stope = cavity

Question 49

Stope mining pros and cons

Answer 49

Pros- less enviro issues and habitat loss can access hard to access reserves cons- more expensive and technical have to pay form ventilation + water pumping + backfilling pumps subsidence risk high e requirement

Question 50

longwall retreat mining SEE BOOKLET FOR DIAGRAM

Answer 50

main shaft dug from surface and tunnels drawn out from shaft 2 roadways drawn to furthest point of extraction asses geo condition prior to mining longwall is established between 2 roadways shaver moves along face slicing coal onto conveyer belt roof held up by hydraulic steel chocks once coal is removed chocks move forward and mined out area collapses retreat towards shaft

Question 51

pros and cons of long wall retreat

Answer 51

pros- can achieve production rates comp to open cast high vol of material low enviro impact and habitat loss cons- high e requirements high tech expensive

Question 52

leaching basic

Answer 52

uses chem sol to dissolve ore from the rock and release target minerals

Question 53

2 types of leaching

Answer 53

in situ leaching at depth heap leaching at surface

Question 54

in situ leaching at depth

Answer 54

boreholes drilled fracture rocks e.g. explosives leaching sol pumped down leaching sol containing ore pumped back up e.g. evaporates extracted using h2o U and Cu using acid

Question 55

in situ leaching pros and cons

Answer 55

pros- less people and machines (cheaper) little disturbance no waste recycle leaching sol cons- toxic

Question 56

heap leaching at surface

Answer 56

same as in situ but material brought to surface crushed to increase SA then heaped on impermeable barrier e.g. clay sol with dissolved mins accumulates in pond taken for further processing

Question 57

heap leeching pros and cons

Answer 57

pros- cheap 60-70% extracted recycle sol cons- takes a long time - months to years

Question 58

froth flotation basic

Answer 58

separates hydrophobic and hydrophilic mins

Question 59

process of froth flotation

Answer 59

ore and H2O = slurry only works if target min hydrophobic add chemical to make it hydrophobic aerate slurry- add O2 hydrophobic minerals attach to air bubbles rise to surface as froth froth collected by skimming rich in target min e.g. produces 70% of the world copper

Question 60

disposal of crushings and tailings post froth floatation

Answer 60

fine grained waste contain toxic min and chems from extraction prev, stored in large surface ponds or disposed of in in underground mines workings or river/sea enviro disaster caused by leakage or may be unstable now legally regulated

Question 61

smelting - reduction of ores specifically iron

Answer 61

sep using heat and reactivity series blast furnace used to extract iron (oxides) carbon (in coal) for more reactive than iron carbon removes O2 from iron - reduced iron isolated

Question 62

problems with mine water

Answer 62

Acid mine drainage

Question 63

acid mine drainage

Answer 63

many mined minerals = sulphide ores empty mines contain fractured rock - exposed/ large SA empty mine is exposed to H2O and O2 react with ores to produce sulphuric acid sulphide min + O2 --> SO2 SO2 + H2O ---> H2SO4

Question 64

treatment methods for AMD

Answer 64

source control migration control active treatment passive treatment

Question 65

source control for AMD

Answer 65

prevent O2 and H2O reaching ore dewater mine- pump out H2O (expensive) or flood and seal with e.g. concrete or clay

Question 66

migration control for AMD

Answer 66

redirect to storage pond for further treatment

Question 67

active control for AMD

Answer 67

adding something to react and neut e.g. alkali - lime CaCO3 OR NaCO3

Question 68

passive treatment for AMD

Answer 68

use nature based system e.g. trickle beds trickle through limestone gravel to neut microorganisms can consume toxic metals sulphides

Question 69

what can be in underground waste storage

Answer 69

chemicals animal carcasses nuclear waste (diff level treated diff) CO2 heavy metal waste rubble-inert municipal sewage waste e.g. collected by council mining waste industrial effluent+ agricultural waste domestic waste

Question 70

advantages and disadvantages of underground waste storage

Answer 70

Pros- space efficient reduces visual impact quick and easy low tech requirements cheap resists structural damage e.g. earthquakes Cons- public opp limited capacity leachate toxic to soil and water bodies produces methane- greenhouse gas and explosive prone to subsidence

Question 71

factors effecting severity of enviro consequence of underground storage

Answer 71

leachate- rain h20 peculates through waste dissolves soluble chems/mins surrounding soil and h20 in aquifers are vulnerable to contam forms pollution plume rock type- impermeable and fine grain e.g. clay resists leachate thick uniform flat beds=best permeable and porous allows leachate to flow limestone dissolved by acid met and ig best only if jointed secondary permeability anticlines- tension joints - increase permeability groudwater- higher WT less distance for leachate to travel to reach underground water

Question 72

levels of nuclear waste

Answer 72

low intermediate high transuranic

Question 73

low level nuclear waste

Answer 73

90% of waste by vol gloves and clothing dep at secure landfill sites grouted in metal containers and super compacted then stacked in concrete lined vault, cap covers when vault is filled some landfills can except V low levels of radioactive waste looking at alt methods e.g. incineration and metal recycling

Question 74

intermediate nuclear waste

Answer 74

7% of waste by vol e.g. reactor comps, graphite from cores cutting, drying and super compacting place waste in suitable container e.g. 500l stainless steel drums immobilise water in cement based materials placed in underground facility or repository geological structure prevents escape of radioactivity or near surface disposal- disposed of close to site as pos

Question 75

high level nuclear waste

Answer 75

3% by vol spent nuclear fuel vitrification-liquid HLW mixed with crushed glass in furnace poured into stainless steel canisters which hold up to 150L creates solid stable product for long term storage held for 50years then dispose of at repository again geological disposal- geo structure insures no radioactivity escapes

Question 76

transuranic

Answer 76

heavy unstable atoms anything above U-92

Question 77

features of underground nuclear disposal site

Answer 77

hard competent rock few faults and joints little seismic activity low WT

Question 78

problem with CO2 + where it anthropogenic emissions come from

Answer 78

acts as greenhouse gas and may lead to acidification of the sea by burning processing fossil fuels manufacturing steel, cement and chemicals

Question 79

how can we prevent CO2 entering atmosphere

Answer 79

carbon capture and sequestration- stored underground react CO2 with metal ions (carbonation)--> form new metal carbonates (stable) --> store capture and compress --> transport via pipelines to underground to depleted gas fields and oil fields saline formations- dissolve C02 combine with rock forming new stable mins

Question 80

examples of carbon capture, storage and sequestration

Answer 80

forest soil e.g. peat bogs ocean graphene production- requires CO2 engineered molecules-changes shape of mol to form new compounds by capturing CO2 grasslands direct air capture biomass carbon removal/capture- use biomass from plant to remove CO2 from air e.g. biooil, biochar, bioenergy carbon mineralisation

Question 81

where is chalcopyrite often found

Answer 81

often found in hydrothermal veins

Question 82

Water sampling

Answer 82

surface or ground water collected surface= reg intervals along river Background metal content few parts per billion (needs to be very sensitive) - seasonal variation must be accounted for increase to a few parts per million may indicate metallic mineral deposit

Question 83

Vegetation sampling

Answer 83

metals taken up by plants through roots analyse trace element content of selected species (biogeochemical survey) collect samples of twigs leaves and seed of chosen plant elevated metal content- indicate underlying mineral dep or geobotanical survey- map distribution of indicator plant species (can tolerate high conc of particular metal in soil) or identify plants with high metal content to locate