Hi. I just need help in answering this questions and diagrams to be drawn. Thank you.
Federation University Australia SCGEO2105 – Economic Geology Practical 3 Radwan Fiezo (30358611) Skarn Deposits for Geos (53 Marks) Introduction Skarn deposits are summarised well in your text (Evans, 1997) however the following website provides an excellent and detailed summary of Skarn Deposits (you can find a link to this site on Moodle) As outlined in lectures, skarns can form through either contact metamorphic, or regional metamorphic processes. The fluid involved in forming skarns can be magmatic, meteoric (percolating rainwater), metamorphic, or even trapped connate water (essentially seawater trapped with the sediments). The key elements to the formation of mineralised skarns are the presence of carbonate host sediments, such as limestone or dolomite, and the presence of adjacent intrusive rocks. Skarns are best developed at the contact between the sediments and felsic intrusives such as granite. Skarns are frequently zoned, with garnet developed proximal (close to) and pyroxene distal (away from) the intrusive rock. Colour variation is often seen to mirror this relationship, with garnet being dark red adjacent to the intrusive body, and increasing green/pale yellow further from the pluton. Not all skarns host economic mineralisation, however skarn deposits, under the right conditions, can be quite rich. In this exercise, you will be examining the Brown’s Creek Gold Skarn Deposit in NSW. In order to successfully complete this exercise, you will need to familiarise yourself with the content of the readings on the Brown’s Creek deposit found in the ‘videos and other resources’ section of moodle for week 3. Classic Skarn development associated with plutons Cu Skarn 1 Federation University Australia SCGEO2105 – Economic Geology Practical 3 Skarn zonation reflects pluton contact geometry as well as carbonate sediment host distribution, and fluid flow regimes. Proximal skarn development is typically garnet rich, while more distal skarn is pyroxene rich. The skarn-sediment boundary may be typified by pyroxenoids (like rhodonite or Wollastonite) or vesuvianite. Table 1 List of common Skarn minerals Mineral Group End Members Composition Garnet Grossularite Ca3Al2(SiO4)3 Andradite Ca3Fe2(SiO4)3 Spessartine Mn3Al2(SiO4)3 Almandine Fe3Al2(SiO4)3 Pyrope Mg3Al2(SiO4)3 Pyroxene Diopside CaMgSi2O6 Hedenbergite CaFeSi2o6 Johannsenite CaMnSi2O6 Fassaite Ca(Mg,Fe,Al)(Si,Al)2O6 Olivine Larnite Ca2SiO4 Forsterite Mg2SiO4 fayalite Fe2SiO4 tephroite Mn2SiO4 Pyroxenoid ferrosilite FeSiO3 rhodonite MnSiO3 wollastonite CaSiO3 Amphibole tremolite Ca2Mg5Si8 O22 (OH)2 ferroactinolite Ca2Fe5Si8 O22(OH)2 mn actinolite Ca2Mn5Si8 O22(OH)2 hornblende Ca2(Mg,Fe)4Al2Si7O22(OH)2 pargasite NaCa2(Mg,Fe)4Al3Si6O22(OH) 2 cummingtonite Mg2(Mg,Fe)5Si8O22(OH)2 dannemorite Mn2(Fe,Mg)5Si8O22(OH)2 2 Federation University Australia SCGEO2105 – Economic Geology Practical 3 grunerite Fe2(Fe,Mg)5Si8O22(OH)2 Epidote piemontite Ca2(Mn,Fe,Al)3(SiO4)3 (OH) allanite (Ca,REE)2(Fe,Al)3(SiO4)3 (OH) epidote Ca2(Fe,Al)3(SiO4)3(OH) clinozoisite Ca2Al3(SiO4)3(OH) Plagioclase anorthite CaAl2Si2O8 albite NaAlSi3O8 Scapolite matialite Na4Al3Si9O24 (Cl,CO3,OH,SO4) meionite Ca4Al3Si6O24 (CO3,Cl,OH,SO4) Question 1. Skarn Minerals. (10 Marks) The presence and zonation of skarn minerals (calc-silicate phases developed from the alteration of carbonate sediments {limestone and dolomite}) are important in recognising and identifying skarn –type deposits. Complete the Table below for the major skarn mineral groups. Mineral Group Hardnes s Colour/Streak cleavage/other Garnet 6.5-7.5 Red/colourless Conchoidal Pyroxene 5-6 Dark Green-Black/light green Two planes not @ 90o Olivine 6.5-7 Olive green Conchoidal Fracture Wollastonite 4.5-5 Colourless-Whit e 2 planes @ <90o 3 federation university australia scgeo2105 – economic geology practical 3 amphibole 5-6 colourless/whit e 2 planes not 90o epidote 6-7 green/colourles s 1 plane plagioclase 6-6.5 white/grey 2 planes @ ~90 and 90 question 2. brown’s creek gold skarn sample bc2 – (10 marks) this sample consists of banded pyroxene and wollastonite (among other minerals) examine sample bc2 and list below the mineral phases and textures observed. also include a labelled diagram of sample bc2 below, including all observed minerals, colours and textures. sample bc2 4 federation university australia scgeo2105 – economic geology practical 3 scale: question 3. sample bc4- (5 marks) high grade gold ore: wollastonite, pyroxene and pyroxenoid minerals this sample is from the main stratabound skarn, and consists of wollastonite, pyroxene + garnet and pyroxeniods. what is the likely gold grade of the remaining mineralised skarn (ie the average grade of the ore reserves) question 4. sample bc4 (2 marks) what other minerals can be identified in the sample question 5. sample bc4 (5 marks) describe sample bc4 include colour, texture, interesting features, structures, veining, and any alteration observed. question 6. sample bc5 (10 marks) sample bc5 is representative of primary high grade ore. sketch and label this sample, paying particular attention to the sulphide mineral phases. include colour, texture, interesting features, structures, veining, and any alteration observed in your description below. sample bc5 diagram 5 federation university australia scgeo2105 – economic geology practical 3 scale: question 7. (3 marks) outline the average gold grade from ore extracted from brown’s creek during production (ie the grade of ore mined in the past) question 8. (3 marks) what are the key host lithologies to mineralisation at brown’s creek? question 9. specimens bc8 and bc9 (5 marks) both these specimens occur in close proximity to mineralised zones, however they are not themselves mineralised. they have been subjected to contact metamorphism but not mineralisation. provide a name for both specimens explaining the basis for your identification. 6 federation university australia scgeo2105 – economic geology practical 3 summary diagram showing the development of a skarn 7 skarn1 skarn2 skarn3 3="" federation="" university="" australia="" scgeo2105="" –="" economic="" geology="" practical="" 3="" amphibole="" 5-6="" colourless/whit="" e="" 2="" planes="" not="" 90o="" epidote="" 6-7="" green/colourles="" s="" 1="" plane="" plagioclase="" 6-6.5="" white/grey="" 2="" planes="" @="" ~90="" and="" 90="" question="" 2.="" brown’s="" creek="" gold="" skarn="" sample="" bc2="" –="" (10="" marks)="" this="" sample="" consists="" of="" banded="" pyroxene="" and="" wollastonite="" (among="" other="" minerals)="" examine="" sample="" bc2="" and="" list="" below="" the="" mineral="" phases="" and="" textures="" observed.="" also="" include="" a="" labelled="" diagram="" of="" sample="" bc2="" below,="" including="" all="" observed="" minerals,="" colours="" and="" textures.="" sample="" bc2 ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" 4="" federation="" university="" australia="" scgeo2105="" –="" economic="" geology="" practical="" 3="" ="" ="" ="" ="" ="" scale: ="" ="" question="" 3.="" sample="" bc4-="" (5="" marks)="" high="" grade="" gold="" ore:="" wollastonite,="" pyroxene="" and="" pyroxenoid="" minerals="" this="" sample="" is="" from="" the="" main="" stratabound="" skarn,="" and="" consists="" of="" wollastonite,="" pyroxene="" +="" garnet="" and="" pyroxeniods.="" what="" is="" the="" likely="" gold="" grade="" of="" the="" remaining="" mineralised="" skarn="" (ie="" the="" average="" grade="" of="" the="" ore="" reserves)="" question="" 4.="" sample="" bc4="" (2="" marks)="" what="" other="" minerals="" can="" be="" identified="" in="" the="" sample="" question="" 5.="" sample="" bc4="" (5="" marks)="" describe="" sample="" bc4="" include="" colour,="" texture,="" interesting="" features,="" structures,="" veining,="" and="" any="" alteration="" observed.="" question="" 6. ="" sample="" bc5="" (10="" marks)="" sample="" bc5="" is="" representative="" of="" primary="" high="" grade="" ore.="" sketch="" and="" label="" this="" sample,="" paying="" particular="" attention="" to="" the="" sulphide="" mineral="" phases.="" include="" colour,="" texture,="" interesting="" features,="" structures,="" veining,="" and="" any="" alteration="" observed="" in="" your="" description="" below.="" sample="" bc5="" diagram ="" 5="" federation="" university="" australia="" scgeo2105="" –="" economic="" geology="" practical="" 3="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" ="" scale: ="" ="" question="" 7.="" (3="" marks)="" outline="" the="" average="" gold="" grade="" from="" ore="" extracted="" from="" brown’s="" creek="" during="" production="" (ie="" the="" grade="" of="" ore="" mined="" in="" the="" past)="" ="" question="" 8.="" (3="" marks) ="" what="" are="" the="" key="" host="" lithologies="" to="" mineralisation="" at="" brown’s="" creek?="" question="" 9.="" specimens="" bc8="" and="" bc9="" (5="" marks)="" both="" these="" specimens="" occur="" in="" close="" proximity="" to="" mineralised="" zones,="" however="" they="" are="" not="" themselves="" mineralised.="" they="" have="" been="" subjected="" to="" contact="" metamorphism="" but="" not="" mineralisation.="" provide="" a="" name="" for="" both="" specimens="" explaining="" the="" basis="" for="" your="" identification.="" 6="" federation="" university="" australia="" scgeo2105="" –="" economic="" geology="" practical="" 3="" summary="" diagram="" showing="" the="" development="" of="" a="" skarn="" 7="" skarn1="" skarn2="">