GEO4910 Field Course 3-4 October 2009

Transcription

1 GEO4910 Field Course 3-4 October 2009 Note: Before you go on the field course, check by yourself the minerals (characteristics, chemical formula) and rocks (mineral content, texture, formation conditions) that we will see (listed below). Participating students must submit their own report from the field course. The report should contain descriptions of the general geology, the way minerals occur, what the rocks look like, their textures and mineral contents, and a discussion on how the mineralizations may have formed, with references to the literature if available. The points below are meant to be of help for the observations and the relevant problems at the different stops. NGT = Norsk Geologisk Tidsskrift (the Norwegian Geological Journal). We will most likely visit the following stops: A, B, C, E, F, G, I, J, L, M. The other stops (D, H, K) are for reserve if time allows. A: Liertoppen Contact between Carbo-Permian biotite granite (the "Drammen Granite") and a contact metamorphosed Cambro-Silurian schist and limestone (both sedimentary rocks transformed to different classes of hornfels rocks). 1. What minerals do you observe in the granite? Use a hand lens and write down the minerals from the most frequent to the least frequent, and estimate their relative abundance in %, and their sequence of crystallization (paragenetic sequence). 2. What texture has the granite? Make a drawing and label the minerals. 3. Look especially at the quartz in the granite. Does all quartz look the same; describe? Could there be two generations of rock-forming quartz in this granite? 4. Use the results from the experimental petrology of Piwinskii (1973), see Appendix 1, to discuss a possible pressure development of this granite, and its bearing on a magmatic water phase in this granite. 5. Do you find signs of fluid circulation (hydrothermal alteration) in the granite? 6. Do you find magnetite (or hematite or other iron-containing ore minerals) in this granite? From this, discuss where the iron could be? B: Gjellebekk / Auvi Mine (Lierskogen) Permian skarn deposit with mainly magnetite, pyrite, chalcopyrite, bismuthinite. 1. What is the geology (rocks, structures) like here? 2. What kinds of skarn minerals (calcium silicates) do you find here? 3. What kinds of ore minerals do you find here? 4. Do you find signs (what/where?) of hydrothermal fluid circulation here?

2 2 C: Prospect by Aas Café (Fiskum-type deposit) Precambrian fahlband / sulfide zone with pyrrhotite and pyrite; cut by Permian hydrothermal vein(s) with sphalerite, galena, chalcopyrite. Late marcacite. 1. What relations do you find between the minerals (paragenetic sequence, replacement reactions)? 2. Do you find any wall rock alteration (type, thickness)? 3. Do you find a black substance in the veins -- what is this substance? 4. Have you got a theory for what kind of geochemical processes led to the formation of this hydrothermal vein deposit? D: Majorplassen (near Aas Café) Hydrothermal quartz veins and fluorite vein of Permian age. 1. Can you say anything about the age relation between the quartz veins and the fluorite vein? 2. Do you find a black substance in the veins -- what is this substance? 3. The quartz in this deposit has fluid inclusions giving salinities of ca. 5 (2,2-6,7) weight % NaCl equivalents and homogenization temperatures of ca. 200 ( ) degrees C with quite constant fluid density of 0,92 3 (0,89-0,96) g/cm. The fluorite gives a larger variation: 0-11 weight % NaCl equivalents (average ca. 8,5) and homogenization temperatures from 115 to more 3 than 355 degrees C with varying fluid density from 0,73 to 1,00 g/cm. Could the quartz and fluorite veins have been formed under similar conditions? 4. Can you provide a hypothesis for the formation of fluorite here? E: Kongsberg Silver Deposit (Kongsberg) Native silver in calcite veins of Permian age cutting Precambrian fahlbands. We will visit the Mining Museum and (if time) a mineralization in the fahlband at Saggrenda. 1. What major / characteristic minerals du you find in the hydrothermal veins? 2. Extent and type of wall rock alteration? 3. Describe the appearance of the fahlband. 4. What are the arguments of Segalstad (2009 and earlier papers) for where the silver came from and how it was deposited? 5. What can be the possible heat sources, which caused the circulation of hydrothermal water in the Kongsberg / Fiskum-area in Permian times? 6. What could have been the complexing agent (ligand) for the hydrothermal transportation of the silver? Where could this ligand have come from?

3 3 F: Nordagutu Granite (Nordagutu) Biotite granite of Carbo-Permian age (contemporaneous with the formation of the Oslo Rift) intruded in Precambrian basement gneissic rocks outside the Oslo Graben. (Jacobsen, S.B. & Raade, G. 1975: NGT Vol. 55, p ). 1. Describe the granite (texture, mineral content, paragenetic sequence), like you did for the Drammen granite. 2. Du you find signs of hydrothermal activity associated with (caused by) the granite? 3. Do you find magnetite (or hematite or other iron-containing ore minerals) in this granite? From this, discuss where the iron could be? G: Cappelen Quarry (Fen; Ulefoss) Carbonatite ("søvite") with columbite and pyrochlore (coppite) etc. of Cambrian age. Damkjernite lamproite (kimberlite-like) dikes. 1. What criteria would you use to characterize the carbonatite as a magmatic intrusive, and not as a sedimentary limestone? 2. What chemical elements have they mined at these quarries / mines and what other chemical elements could be of economic interest from here? H: Road cut and Vaskeriet (Fen; Ulefoss) Ferro-carbonatite and rødberg (red carbonatite) with hematite and REEminerals of Cambrian age (REE = Rare Earth Elements; the Lanthanides + yttrium). 1. Do you see signs of post-solidus volatile activity in the carbonatite? 2. What chemical elements have they exploited from the rock "rødberg", and what other chemical elements could be of economic interest from here?

4 4 I: Gautefall Tourist Hotel (Telemark) - night quarters The Tørdal Granite, age ca. 1 billion years. 1. Describe the granite's appearance compared to the Drammen- and Nordagutu granites. You see that there is almandite garnet in the granite. Is this a common primary magmatic mineral? What could be the reason for finding almandite in this granite? 2. Granites may roughly be classified into mantle-derived and anatexisderived (earlier called palingenetic) granites, the latter formed by ultrametamorphosis. Anatexis-granites may further be subdivided into I-type (re-melted igneous material) and S-type (melted sedimentary material). In some cases "restites" (unmelted rests of the original rocks) can give information about the origin. From your observations and this very simplified way of classification, would the Tørdal Granite be resembling an I-type or S-type granite? [There are other proposed granite classifications, like anorogenic "Atype" and rift-related "R-type" granites, that will not be considered here.] 3. Do you see signs of hydrothermal activity associated with (caused by) the granite? 4. Burnham & Ohmoto (1980) argued that especially copper deposits would be associated with I-type granites, and that especially tin deposits would be associated with S-type granites. Molybdenite deposits may be associated with both types. If Burnham & Ohmoto (1980) were right, what kinds of deposits would you expect to find in the area associated with the Tørdal granite? See Appendix 2. Reference: Burnham, C.W. & Ohmoto, H. 1980: Late stage felsic magmatism. Mining Geology, Special Issue, No. 8, p J: Tørdal (central Telemark) Precambrian granite pegmatite associated the Tørdal Granite with amazonite alkali feldspar, beryl, topaz, lepidolite (Li-mica), cassiterite and REE-minerals. 1. Describe the relations between the pegmatite and its wallrocks. 2. Describe structure (zoning?) of the pegmatite (wall zone, graphic granite zone, core-wall zone and core zone). In which zones do the different pegmatite minerals occur (dominate)? 3. Do you find any hydrothermal veins cutting the pegmatite -- if so, where do these veins originate? J (alternative): A pegmatite quarry, Kragerø (southern Telemark)

5 5 K: Kragerø (southern Telem ark) Precam brian albitite (kragerøite) with rutile, pegm atite veins, apatite veins, hem atite veins. 1. Describe the geologic appearance. 2. Bodart (1968) proposed a metam orphic / m etasom atic model for the form ation of ore deposits in the Kragerø Area. G ive a sum m ary of Bodart's m odel. W hat is your opinion about Bodart's model for the explanation of the Kragerø Area's geology judged from your observations? Reference: Bodart, D.E. 1968: O n the paragenesis of albitites. NG T Vol. 48, p L: M eikjæ r Nickel M ine (Bam ble) [or another nickel m ine in this area] Precam brian noritic gabbro with m assive sulfides Describe the geologic occurrence of gabbro and m assive sulfides. W hat is the texture of gabbro and sulfides? W hat m inerals do you find in the gabbro? W hy is the gabbro called a norite? W hat ore m inerals do you find? Do you find the nickel m ineral pentlandite? How does it occur? Are there any late-stage alterations of the ore? po ptl ptl po cp Meikjær Mine vio po cp cp po vio Nystein Mine Photomicrographs, Bamble nickel ores, polished sections, 0.5 mm longest side. Left: Meikjær Mine; pentlandite (ptl) in pyrrhotite; cp = chalcopyrite. Right: Nystein Mine; pentlandite (ptl) replaced by violarite FeNi2O4 (vio) in pyrrhotite (po). Photo and collection: T.V. Segalstad. If pentlandite (Fe,Ni)9S8 is written as simplified FeNiS2; possible replacement reaction: 2 FeNiS2 + 3 H2O O2 = FeNi2O4 + Fe2+ (aq) + 6 H+ + 4 SO42- (aq).

6 6 M: Tvedalen (Vestfold) Larvikite monzonite quarry, building and ornamental stone 1. What minerals do you observe in the larvikite? Use a hand lens and write down the minerals from the most frequent to the least frequent, and estimate their relative abundance in %, and their sequence of crystallization (paragenetic sequence). 2. What texture has the larvikite? Make a drawing and label the minerals. 3. Do you find quartz in the larvikite? If not, is there another mineral present instead of quartz? 4. The larvikite is an attractive decorative stone because of its multi-colored "Schiller Effect". Is this effect present in all orientations of the rock? 5. Do you see any pegmatites in the larvikite? What major minerals do these pegmatites carry? Are these pegmatites different from granite pegmatites; if so, in what ways? What kind of pegmatites are these? Report: The report is due 2 days after the field course (Wednesday). The report should be based on your field observations, our discussions in the field, and the literature handed out (plus other literature you may find relevant). The report doesn't need to be extensive or neatly made. Answers to the questionnaire, handwritten and drawn on the front and rear pages of the questionnaire itself, will be accepted.

7 7 What to bring to the field course: Useful to bring: Hammer, chisel, hand lens, protection eye glasses, sample bags and marker pen if you plan to collect samples, notebook, writing materials, geologic maps, clinometer compass, magnet, acid bottle with 10% HCl, pocket knife, field backpack, the textbook plus handouts from the GEO4910 course. In addition bring: Sturdy field boots, wind- and rain proof field clothes, warm clothes / long underwear, neat clothes and possibly swim suit (for the hotel). Food: Bring a lunch bag (or more than one?) and what you want to drink for the first day. The course offers a LATE dinner (at about 20 o'clock) the first day, plus breakfast and lunch the second day. Transportation: 16 seat mini-bus. Inside the vehicle the following is prohibited for safety reasons: smoking, food, glass bottles, loose rock samples, and loose hammers / chisels will be prohibited. All loose things must be put in your luggage or in the plastic boxes provided. (If you want to collect samples, you must bring sample bags etc. yourself). Departure from Oslo the first day around 8 o'clock (places or be agreed on); return the second day at o'clock (?). Night quarters: Gautefall Tourist Hotel (Gautefallheia near Drangedal, central Telemark County). Phone: / Note: The course pays for the hotel accomodation and the meals. But all extra expenses (like drinks or telephone at the hotel) will have to be paid by the students before departure! The hotel pool is normally open between 7 and 20 o'clock. Sunday morning breakfast at 8 o'clock and departure no later than 9 o'clock. Mobile phone: The teacher Segalstad has cellular phone # for important incoming messages. Some parts of the field course have no cellular phone coverage (but messages can be left at the answering machine, and the calls can be returned later). 2. October 2009 Associated professor Tom V. Segalstad Geological Museum, University of Oslo

8 8 APPENDIX 1 The line colored red indicates the stability of quartz in the granitic melt. Quartz (Qz) is stable to the right and above the red line. By cooling the melt, or lowering the water pressure in the melt, the quartz will no longer crystallize from the melt to the left or below the red line ("Qz out"). Similarly for the other major rock-forming minerals plagioclase (Plag) or potassium feldspar (Kspr). The granitic melt is completely solidified to a granite at the solidus curve.

9 9 APPENDIX 2 Excerpted from (with chemical reactions added): Burnham, C.W. & Ohmoto, H. 1980: Late-stage processes of felsic magmatism. Mining Geology, Special Issue, No. 8, p

10 10 APPENDIX 3 The main field trip stops indicated on the Bedrock Map of Norway, Norwegian Geological Survey, Scale: width of map ~140 km. North = up. Reference to the bedrock map: Sigmond, E.M.O., Gustavson, M. & Roberts, D. 1984: Berggrunnskart over Norge - M. 1:1 million. Norges Geologiske Undersøkelse, Trondheim.