(pdf 3.5 MB) - Erich U. Petersen

Guidebook
Field Mapping in Porphyry Copper Environments
Cerro Colorado Mine, Chile
August 11-14, 2002
Erich U. Petersen
College of Mines & Earth Sciences
University of Utah
Salt Lake City, UT
William X. Chávez, Jr.
New Mexico School of Mines
Socorro, NM
Acknowledgements
We wish to acknowledge the many individuals and organizations that made this
course possible. We thank Compania Minera Cerro Colorado (BHP Billiton) for granting
generous access to the Cerro Colorado Mine . Ing. César Otarola and Ing. Eduardo
Fernandez provided invaluable help in organizing the course. The cover photo was taken
in 1997. The mapping course is sponsored by the Society of Economic Geologists.
Erich U. Petersen
Department of Geology and Geophysics
The University of Utah
135 S. 1460 E., RM 719
Salt Lake City, UT 84112-0111
801-581-7238
William X. Chávez, Jr.
Minerals & Environmental Engineering
Department
New Mexico School of Mines
Socorro, NM 87801
505-835-5252
[email protected]
http://www.mines.utah.edu/pyrite
[email protected]
Field Mapping in Porphyry Copper Environments
Participants
1. Carlos Caceres
[email protected]
2. Cristian G. Calderon S.
3. Jose Cardenas P.
[email protected]
4. Julio Cordova P.
[email protected]
5. Eugene Cox
[email protected]
6. Jean-Philippe Desrochers
[email protected]
7. Amy Eichenlaub
[email protected]
8. Ralph Gonzalez
[email protected]
9. Takeshi Harada
[email protected]
10. Ann Pattison
[email protected]
11. Carmen Quispe
[email protected]
12. Gustavo Rodriguez
[email protected]
13. Samantha Roffey
[email protected]
14. Fernando Rojas Angel
[email protected]
15. Alejandro Sanhueza
[email protected]
16. Carlos Urrutia
[email protected]
17. Javier Urrutia
[email protected]
18. Percy Zamora Diaz
[email protected]
Itinerary
11 August, Sunday
11:00 AM
1:00 PM
5:30 PM
Airport Pickup, Drive to Mamiña (Refugio del Salitre)
Depart Holiday Inn Express for Mamiña (Refugio del Salitre)
Organizational meeting
12 August, Monday
6:30 AM
7:00 AM
7:30 AM
9:00 AM
1:30 PM
1:30 PM
5:00 PM
Breakfast
Depart from Mamiña for Cerro Colorado
Check in at Cerro Colorado, Mine Safety
Mapping I
Lunch
Mapping II
Depart Cerro Colorado for Refugio del Salitre
Evening Session
13 August, Tuesday
6:30 AM
7:00 AM
7:30 AM
1:30 PM
1:00 PM
5:00 PM
Breakfast
Depart from Mamiña for Cerro Colorado
Mapping III
Lunch
Mapping IV
Depart Cerro Colorado for Refugio del Salitre
Evening Session
14 August, Wednesday
6:30 AM
7:00 AM
7:30 AM
1:30 PM
3:00 PM
Breakfast
Depart from Mamiña for Cerro Colorado
Mapping V: Leached Capping / Core Review
Lunch
Depart for Airport
Useful References
Billings, M.P., 1972, Structural Geology, third edition, Prentice Hall, New York, 606 p.
Chávez. W.X., Jr., 2000, Supergene Oxidation of Copper Deposits: Zoning and
Distribution of Copper Oxide Minerals. SEG Newsletter No. 41, April 2000.
Compton, R.R., 1985, Geology in the Field. John Wiley and Sons, New York, 398 p.
Davis, G.H., 1984, Structural Geology of Rocks and Regions. John Wiley and Sons,
New York, 492 p.
Phelps Dodge, 2000, Geologia de los Porfidos de Cobre Cerro Verde Y Santa Rosa,
Arequipa, Peru. Departamento de Geologia, 21 p.
Pierce, F.W and Bolm, J.G., Eds., 1995, Porphyry Copper Deposits of the American
Cordillera. Arizona Geological Society Digest, 20, 656 p.
Titley, S.R., Ed., 1982, Advances in Geology of the Porphyry Copper Deposits,
Southwestern North America. University of Arizona Press, Tucson, AZ, 560 p.
Titley, S.R. and Hicks, C.L., Eds., 1966, Geology of the Porphyry Copper Deposits,
Southwestern North America, University of Arizona Press, Tucson, AZ, 287 p.
Some Common Mineral Formulas
Chlorite ..................................... (Mg,Fe)3(Al,Si)4O10(OH)2.(Mg,Fe)3(OH)6
Biotite........................................ KFe3AlSi3O10(OH)2
Muscovite.................................. KAl3Si3O10(OH)2
Kaolinite.................................... Al2Si2O5(OH)4
Alkali feldspar........................... (K,Na)AlSi3O8
Plagioclase ............................... CaAl2Si2O8
Dumortierite.............................. Al7O3(BO3)(SiO4)3
Tourmaline................................ (Na,Ca)(Li,Mg,Al)(Al,Fe,Mn)6(BO3)3
(Si6O18)(OH)4
Bornite ...................................... Cu5FeS4
Chalcopyrite.............................. CuFeS2
Chalcocite ................................. Cu2S
Covellite.................................... CuS
Cuprite ...................................... Cu2O
Tenorite..................................... CuO
Minerals Commonly Found in the Oxide Zone of Copper
Deposits
Alunite ........................................................... KAl3(SO4)2(OH)6
Antlerite ......................................................... Cu3SO4(OH)4
Atacamite (paraatacamite, botallackite) ........ Cu2Cl(OH)3
Bonattite......................................................... CuSO4.3H2O
Brochanite...................................................... Cu4SO4(OH)6
Ceruleite......................................................... Cu2Al7(AsO4)4(OH)13.12H2O
Chalcanthite ................................................... CuSO4.5H2O
Chalcosiderite (compare to tourquoise)......... CuFe6(PO4)4(OH)8.4H2O
Chenevixite .................................................... Cu2Fe2(AsO4)2(OH4.H2O
Chrysocolla (mineraloid) ............................... Cu(Fe,Mn)Ox-SiO2-H2O, with
copper content varying from
~20-40 wt % Cu
Copiapite........................................................Fe5(SO4)6(OH)2.20H2O
Coquimbite..................................................... Fe2(SO4)3.9H2O
Goethite.......................................................... a-FeOOH
Jarosite ........................................................... (K,Na)Al3(SO4)2(OH)6
Kröhnkite ...................................................... Na2Cu(SO4)2.2H2O
Levandulite .................................................... NaCaCu5(AsO4)4Cl.5H2O
Libethinite...................................................... Cu2PO4(OH)
Paramelanconite............................................. Cu4O3 (see tenorite (CuO) and
cuprite (Cu2O)
Poitevinite ...................................................... (Cu,Fe,Zn)SO4.H2O
Posnjakite....................................................... Cu4SO4(OH)6.H2O
Pseudomalachite ............................................ Cu5(PO4)2(OH)4
Scorodite ........................................................ FeASO4.2H2O
Turquoise ....................................................... CuAl6(PO4)4(OH)8.4H2O
Voltaite........................................................... K2Fe8Al(SO4)12.18H2O
Wroewolfeite (Langite).................................. Cu4SO4(OH)6.2H2O
SEG Field Mapping Course-- Cerro Colorado
Petersen & Chávez
Exercise:
Collection and Interpretation of Structural Data using "Titley Squares"
Ejercicio:
Recolección e interpretación de datos estructurales usando "Cuadros Titley"
This exercise asks one to collect standard fracture density information - but with
the caveat that we will quantify the structural data obtained using the methods described
by Heidrick and Titley (1982). The method is this: using squares having dimensions of
50 cm by 50 cm, one collects the total length of fractures occurring in four orientations.
These directions are up-down, left-right, and the two diagonal directions. One sums the
total fracture lengths measured, and divides by the total area of the square, or 2500 cm2.
This gives a quantitative value of fracture occurrence, as given in length/area, having
therefore units of (length)-1. Note that one measures all fracture types, including veinlets
of various types, as well as "clean" fractures.
This information is collected at various areas within the mine, and point values in
(length)-1 are plotted and contoured (as at Sierrita, Arizona; Titley, 1999), showing the
spatial changes in fracture density within an ore deposit, or within a specific intrusion or
rock unit.
For this exercise, please measure - and compare your measurements - the fracture
densities for each of the "Titley Squares" we have prepared. Can you explain the
variation in fracture densities observed, even though we measured only a small area of
the mine?
En este ejercicio, medimos, en una manera quatitative, la densidad de fracturas en
cuadros nombrados "Titley Squares" (véase Heindrick and Titley, 1982). La idea medir
el largo de fracturas (fracturas abiertas, vetillas) dentro de un área cuadrada, en este caso
50 cm por 50 cm, ó 2500 cm2. Calculamos entonces la razón: (largo total de fracturas)
dividido por (área del cuadro), que nos da un número en (largo)-1.
Este número se pude plotear, como una inicación de la distribución de la densidad
de fracturas según área en el yacimiento ó el prospecto, asi como hecho Titley en el
yacimiento tipo pórfido de cobre Sierrita (1999).
Al plotear estos datos de la Mina, ?por qué hay una diferencia importante en la
densidad de fracturas que hemos medido, a pesar de que el área del yacimiento que
hemos estudiado es realtivamente pequeño?