FILE_4174

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University of Colorado, Boulder *

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1030

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Geology

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Feb 20, 2024

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CHTON1\V I Y (1o W Y T dAc) 2~ L 85% =) Q (€7To) [oTe | VA (VIO N1 oToT =) (o] g YA\ ETo IVE IR WIa A=Y £71 4V o] f 0Fe] (o] 2= To [ M =10 B AV 4)) Q | m | Name M ﬂ an& (\Ob"\ ;/)] Lab I — Jamestown Our goals for today’s lab are three-fold. First, we want to decipher the story of Colorado’s Proterozoic tectonic setting that the rocks exposed in Boulder’s foothills have to tell. Second, we want to examine the effects that the Paleogene intrusion of both magma and hydrothermal fluids had on those Proterozoic rocks. The reason — that event produced all the valuable metals that so influenced Colorado’s history. Finally, we want to explore the environmental legacy of mining here, a full 150 years after the first mines opened. Question L1: As always, we need to place our geological observations into their proper geographic context, so please use a yellow highlighter to trace the route of our field trip on the map shown in Figure I-1 (Figs. I-2&3 should help you locate the stops). Mark each stop accurately on the map with a small, neat dot and draw an arrow from the dot to a circled number for each stop (1 for the first stop, 2 for the next, etc.). ‘\'rw - S-[a(t = Stop 1- Boulder’s Proterozoic tectonic setting (Answer questions L2-L9 at this stop) l V‘l’\ m Two different rock types exist in the road cut on the north side of the road at this stop, one j s metamorphic. The van has U\I/ pulled out on the south side of the road. Take in the ‘big picture’ view of this outcrop from the van, then garefully cross the road to examine the outcrop in more detail. The questions for this stop ask you to identify both ge€k types, deteffihg their ages, and use their characteristics to decipher Boulder’s tectonic setting when these rocks formed. Question L2: Draw a ‘big picture’ sketch of the outcrop as seen from the van. Be sure to igclude both ofhe rock types that exist here. After you have identified each rock type (see the following questions), label each type on youl~sketch. B2 sure to include a scale. Question L3: Examine up close the rock that cuts from upper left to lower right across the oufcrop. You will find this igneous rock is composed white, pink, and silver mineral crystals. As you examine this rock and its minerals, pnsyer the following: . ot a. What is the maximum size of an individual crystal in this rock? ‘«\(OJ/ M Pime e Mg |ovgpp oKX Qbod B indrS A b. Based solely on the unusually large size of the crystals, what rock type is this? Whrusive 1Qness c¢. What mineral forms the white crystals? Explain how you identified it. (r)e,m quz et e of W whnike cmyllv"b O kg b FERe U /\/

CHTON1\V I Y (1o W Y T dAc) 2~ L 85% =) . Q N d. What mineral forms the pink crystals? Explain how you identified it. Wt Hrine Mdspar boy A ontit OV coior e. What mineral f'orms the sﬂver crystals’ Explaln how you 1dent|f' ed it. e . ased on the texture e rock to what sub-class of 1gneous roc does this rock belong, intrusive or extrusive? Support your answer. (Vi b( ot trhas '(y? [ ot o WU s fie pawed €. ly /WS g sofad g g. Based on both the color of‘Mé1 rock aqg on e minerals it contalnspev'hat is the‘:fenmy ohils rock type at':he third le."f of igneous rock classification? Support your answer. W€ lpeheM s LN e Covize oF 7 ( e olor ard —\-kt oo/ oty Gnd iés (ye ¢ come of o Question L4: Examine up close the I%MC roclr(\vlth the vertical fabrlc that forzlr% #Cftheyou rop (ever}thlng except the ( rock that cuts from left to right that you described in Question 3). As you examine this rock, answer the following: UWM[I a. Based on the texture of the rock, to what sub-class of metamorphic rocks does this rock belong, foliated or non-foliated? Support your answer. T4 (f foli Ld lbe CAwT i+ :J’ﬂ)"”' LMO‘( and (o e .«F ees o Lol b. What is the identity of this rock type at the third level o metamorphlc rock classification? Support your answer. TS SN b e 17 fsliche® anck hov laagvriolc crynals . Our next task is to determine when these two rocks formed. Recall (from Lab C) that numerical rock ages are determined using radiometric dating techniques. The radiometric age marks the time the rock cooled below the blocking temperature. For igneous rocks, that age is effectively the time the rock solidified. For metamorphic rocks, it could be the age of metamorphism (if the temperature of metamorphism exceeded the blocking temperature) or the age of the protolith (if the metamorphic temperature was below the blocking temperature). It turns out that the ages of both the igneous and the metamorphic rocks in this outcrop are nearly the same and that the age of the metamorphic rock represents the age of metamorphism (i.e. the metamorphic temperature was very high, above the blocking temperature). H L hand M Sine e Question L5: A geologist extracts a sample of the mineral zircon from each rock type in this outcrop agd processes them in order to el use the U-Pb radiometric dating technique. She confirms that the zircon crystals from both samples rgained closed chemical systems. ot Using her mass spectrometer, she measures the daughter-to-parent ratio between the 2**U paren pe and the 2°°Pb daughter isotope in both samples. She finds that the daughter to parent (D/P) ratio in both samples is the same a (i.e. 0.38 half-lives of >**U has elapsed since each rock formed). The half-life of 2%U is 4.47 x 10° years (4.47 billion years). Calculate the age of both rocks. Please show your mathematical work. Y yrx = W v gquq h\lO" lbqg 90 l

3:51 PM Mon Mar 29 2~ L 85% =) Q (€7To) [oTe | VA (VIO N1 oToT =) (o] g YA\ ETo IVE IR WIa A=Y £71 4V o] f 0Fe] (o] 2= To [ M =10 B AV 4)) Q | m | Now that you have identified both rock types present in this outcrop and the time that they both formed, we want to use their characteristics to determine what was going on tectonically in the Boulder area at that time in the Proterozoic. Outcrops of both the igneous and the metamorphic rocks you see here are common throughout the mountains of Colorado from Boulder to Durango. An identical suite of rocks (same characteristics and age) is found across northern Arizona (for example, at the bottom of the Grand Canyon). Question L6: Given the characteristics of these metamorphic rocks (i.e. Question L4) and their regional extent, what type of plate tectonic boundary likely existed here at the time these rocks were metamorphosed (divergent, convergent, or strikf-slip)‘? List the reasons for your conclusion. C MM we /e mftmouhiL rouc gyc o QbwidCnt gf- Yt re prevr It is desirable to determinebtmcfigl‘i‘tfi'or any metamorphic rock (i.e. the type of rock that was metamorphosed). For rocks that were metamorphosed at the very high temperature and pressure that these were, it is not easy to determine the protolith from visual inspection alone. But geologists who have done laboratory tests on this rock have discovered that the protolith was a stack of interbedded sandstone, mudstone, and volcanic ash. Question L7: a. What type of volcano erupts volcanic ash? COMmpocit | Shabo Vol cares b. This volcano type is common at what type of plate boundary? Qﬂ( (orignt SUOAN Uion 2ot g, Chomber oo Py Question L8: Given the characteristics of the igneous rock here at Stop 1 (Question L3): > i /\J'O f'ld. Lol ¢ a. What type of geologic feature does this rock likely represent? Explain your reasoning. A ol @0 o ~4Grma passir o Y OcCt g Cuse Garint Comes Aormrmafma, . _ b. At what type of plate boundary did these rocks likely form? Explain your rea'soning. . o s wd*w 1o Alnosit- at( qetni & vy af Conveent- bodanty hecande v oL a\'al'hM/m Question L.9: Considering your answers to Questions L6-L8, describe the tectonic setting of Boulder in the early Proterozoic, when these rocks formed. In what direction was the plate boundary oriented at that time? Describe the evidence you used to reach your not forry conclusions. . o~ 1oL A~ o s S * NO'/WOLJJ' Alft(,‘hmn A St et raXom i oLk ¢ Ulake bourrasy, TGk Rourdt Ineve N Cavred 1y h%o/f";’fi onAfram GeirY ja @ Nigw pres cdodvhev 1one 91

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3:51 PM Mon Mar 29 2~ L 85% =) Q (€7To) [oTe | VA (VIO N1 oToT =) (o] g YA\ ETo IVE IR WIa A=Y £71 4V o] f 0Fe] (o] 2= To [ M =10 B AV 4)) Q | m | ¢ L“\‘L:,,\’t\v" yhorpIie o PE) :! \ W Stop 2 — The effects of Paleogene igneous activity on pre-existing rocks (Answer questic?ns L10-L13 at stop) The van will park on the left side of the road at Stop 2. The outcrop on the right side of the road consists of the same/fock types as U/O those you examined at Stop 1. Take in the ‘big picture’ view of this outcrop from the bus, then carefully cross the road to examine the outcrop in more detail. The questions for this stop ask you to identify the ways the rocks here resemble those of Stop 1, the ways they differ, and the reasons for those differences. '|1‘ NV Question L10: Draw a ‘big picture’ sketch of the outcrop as seen from the bus. Be sure to include both of the rock types that exist d' (73 here. After you have identified the various rocks present (see the following questions), label each type on your sketch. Be sure to include a scale. .. rw 1 = igngoy, e 1: Mol Most of this outcrop consists of the same metamorphic rock as that you observed at Stop 1. There are also several dikes of the same igneous rock as that at Stop 1 as well. Question L11: Locate the dikes of igneous rock and answer the following: a. Identify three minerals present in this igneous rock and describe the properties you used to identify them. j« Warkz , pprHowy Eeldl pov dngh yr! P e (gt Phy afuLome 3l sTp L s rock” b. What is the maximum Crystal size of the minerals in thi c. Be sure to label these dikes on your outcrop sketch (Question L10) Question L12: Although the rocks in this outcrop are the same ones present at Stop 1, they have been altered. Look for this rock alteration and answer the following: a. What is the primary evidence of rock alteration visible in this outcrop? . [low discolomBan e caue s tunate Howivg Hvogly, b. What type of metamorphism caused this rock alteration? Conjat e mmovphi /- c. Be sure to label on your outcrop sketch (Question L10) the areas of the rock outcrop that have undergone particularly strong alteration. Question L13: The prospectors of the 1800’s searched the hills of Colorado looking for ‘color’, the term they used to describe altered rocks that might contain valuable metal ore. Keeping that in mind, answer the following: a. Would the 19" Century prospectors find this outcrop to be worth their time to examine carefully? Why or why not? \‘(“- | i oA B2 v (A'MM‘:'? becve Hnefe ey cottin avan\sfiy o Colors, mch 1S Whak ey s (oony Ay,

3:51 PM Mon Mar 29 2~ L 85% =) Q (€7To) [oTe | VA (VIO N1 oToT =) (o] g YA\ ETo IVE IR WIa A=Y £71 4V o] f 0Fe] (o] 2= To [ M =10 B AV 4)) Q | m | Wikt Hay ik loe Comse e e Si0L VdOdes Orostie) andd F(GtFe =ik g gy, by, : ar ‘ i v : C(/\'\bv d 2 amww b‘r oL .. &M”fyan({-w o ke oy\%‘q?&\#- Q, b. Are there any signs that the old prospectors did in fact examine the rock here carefully (pay particular attention to the left side of the outcrop)? If so, please describe the evidence. c. If your answer to part b) is yes, are there signs that prospectors discovered valuable ore in this outcrop? Explain your reasoning. (ye Cwe ovr%-(,qu Kﬂ.y Ol'lﬂMAm Yo e conndsee it € boleee Stop 3 — The environmental legacy of Jamestown mining (Answer Questions L14-L16 at this stop) The van will park for Stop 3 at the junction of James Canyon Drive and Balarat Road (County road 87). The parking area lies very close to three of the major Jamestown mines, the Argo, the Burlington, and the Emmit. From the parking area we will walk about 200 yards down James Canyon Drive to examine the Emmit Mine. An old shaft, shored up by timbers, lies immediately west of the road. A small amount of water is seeping out of the shaft. It flows under the road and empties into Little James Creek 50 yards east of the road, right next to a tailings pile from the Burlington Mine. Question L14: Your instructor will show you some rock samples from the Emmit Mine. a. What is the purple mineral in this sample? To what mineral group does it belong? € lowalkt ) hatite neneal b. This was a principal ore mineral during the later Jamestown mining history. What element was extracted from this mineral and what was it used for? Vi) v (hmifedhbrr A Jre o Al e ( vle | Question L15: Use the pH paper or meter provided by your instructor to measure the pH of the water draining from the Emmit mine. a. What is the pH of this water? b. Given the pH you measured here,%;w many times more acidic or alkaline than pure, distilled water is the water draining 0 . from the mine? Nnevad =) = ‘oA be ‘05 - 109,90 c. Describe the color of the material over which the water flows here. What is causing the material to take on this color? T Celor i€ nwa{p(y Do ond OVIAGRoA U pearnvy, (Owng iy ot (olar o LMW,," d. Consider your answers to parts a-c above in the context of what you know about the chemical reactions between sulfide minerals, which were mined here, and water. Based on your observations and on your theoretical knowledge, do you suspect the potential for environmental hazards here that you cannot detect directly? If so, what are those hazards and why do you suspect them to be present? ey bbcame e v S wd?“f-y h'\qh(., QUi C M b Aans o cahon ir rcient=. Mgty cat? e fncs o of o vate floy o InetAal , whith odd &0t i igin mtda | tontrrt{a i ccuter.

3:51 PM Mon Mar 29 2~ L 85% =) Q (€7To) [oTe | VA (VIO N1 oToT =) (o] g YA\ ETo IVE IR WIa A=Y £71 4V o] f 0Fe] (o] 2= To [ M =10 B AV 4)) Q | m | 766 A~ Question L16: Cross the road and examine the tailings pile immediately to your east. a. Sketch the tailings pile and its surroundings. Remember to include a scale. b. Estimate the proximity of the tailings to Little James Creek. fi’m ¥4 loar prekty tore m..(,a(aaz otof [0=20 feet c. Discuss any potential environmental concerns you hdve based on your observations here. I e e i/ Vi ¢ (0ce 4oL m?p(,u-h’ckcodd w2 |t Tl Leoke . unofs co Al Go ! Lo (e Stop 4 — The egfvironmental legacy of Jamestown mining (Answer Questions L17-L18 at this stop) Wi downbaliAamm Me The van will park at Stop 4 in downtown Jamestown, immediately beyond the post office. From the parking area walk the short W"A distance to James Creek. This site is just below its confluence with Little James Creek. Question L17: Use the pH paper or meter provided by your instructor to measure the pH of the water in James Creek here. a. What is the pH of the creek here? CH= b. Compare the pH you measured here with that you measured coming from the Emmit mine at Stop 3. Discuss your working hypothesis/hypotheses for any pH difference you find between the two sites. . ™iJ bty i5 ot meubvad wind aF He eradt Nedhatl onben while it oftee wa. et c. Given the results from your very small pH sampling study, design a pH monitoring program that would be comprehensive enough to provide sufficient data on which to base a decision regarding whether or not any environmental remediation is necessary in order to protect water quality in the Jamestown/Lefthand Canyon area. Outline your plan, including where you a&t¢igl, ¢ would conduct pH sampling, the minimum number of sampling sites you deem sufficient for the study, and when and how be; frequently you would sample the water. Justify your selections in each case. od- nvironmental monitoring has shown that multiple sites along both Little James Creek and James Creek possess elevated 2 . concentrations of a variety of heavy metals. These sites are also devoid of aquatic life. As we discussed in the Pre-lab, Lefthand Creek, into which James Creek flows 3 miles downstream, provides water for 15,000 Boulder County customers of the Lefthand Water District. Pre-lab Question 13 asked you to comment on the appropriate role of science in the process of deciding whether or not environmental remediation is warranted on Lefthand Creek. Consider your analyses today and your thoughts on that question as you answer Question 18. P o WA L nonifor wiarker b cvery I\May ard aftr ¢|,‘/\JHA‘\( ainr V;’\’| of Ko = Comppean katin e uhan | wnich PH 7 Se e tanm WU+ 4 iy WOFE Oy ’ de” - i o4 Jy iF o mafre IS o £iky = ewun Sk i vicolfor (annmphion Safc [hoo midichs oAAn

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3:51 PM Mon Mar 29 2~ L 85% =) Q (€7To) [oTe | VA (VIO N1 oToT =) (o] g YA\ ETo IVE IR WIa A=Y £71 4V o] f 0Fe] (o] 2= To [ M =10 B AV 4)) Q | m | Question L18: Assume that you are a customer of the Lefthand Water District. The Board of Directors asks for your opinion regarding the District’s water quality and the course of action they should take regarding potential heavy metal contamination of the District’s water. They propose three options: Option 1: Maintain the status quo, conducting water quality monitoring consistent with that done by any normal water district. There is no cost to you if this option is selected; your water rates will remain unchanged. Option 2: The District funds a comprehensive environmental study to obtain information on threats to the District’s water quality beyond what the EPA has already determined. The cost of this option to you is a 5% increase in your water rate. Option 3: The District sells bonds in order to fund immediate, comprehensive environmental remediation of all sources of heavy metal contamination along Lefthand, James, and Little James creeks. The cost of this option to you is a 25% increase in your water rate. a. Do you have concerns about the potential safety of the water you drink? ¢ ke (ave ofHC hi&y\ wtal Lnftnt Ko He acdi - b. Which of the above options would you urge the Board of Directors to select? Explain why you selected the option that you did and the role the science played in your decision. Discuss how you factored the personal economic cost to you against other factors. Note that there isn’t a “correct” option to choose. We are looking for you to provide a thoughtful answer that explains why you selected the option that you did, whichever one you chose. (e Clrooie opon 2 e o lHeeghn if JW“M“JMM lee Wnobvok Waryone s mgre b Py For s aption funpane Opbon T migrt pe Nt afddavic ot also vvw/by:j +» ﬂef“n'd”;'f"‘e - 95

3:51 PM Mon Mar 29 2~ L 85% =) Q (€7To) [oTe | VA (VIO N1 oToT =) (o] g YA\ ETo IVE IR WIa A=Y £71 4V o] f 0Fe] (o] 2= To [ M =10 B AV 4)) Q | m | wsme p— e — soame omme rome Wass4 Zon 197 ez " = + . S\ )- i &2 0%& s = 1 =t NATIONAL S "‘ VW GEOGRAPHIC & s : ey Loiron Figure I-1 96

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