MINERALOGICAL AND COMPOSITIONAL ANALYSIS OF TURQUOISE ARTIFACTS LINKED TO ...

372 Pages·2011·36.56 MB·English

MINERALOGICAL AND COMPOSITIONAL ANALYSIS OF TURQUOISE ARTIFACTS
LINKED TO PREHISTORIC MINES IN NEW MEXICO, USA
by
CYNTHIA HOTUJEC
(Under the Direction of Samuel E. Swanson)
ABSTRACT
Petrography, Electron microprobe analysis, and X-ray diffraction analysis of thirty
turquoise samples from four mine locations compared to ten artifact samples demonstrates that
major element chemistry of the turquoise mineral group members is a potential indicator of
geologic source. Mineralogical heterogeneity of turquoise has historically complicated attempts
at determining the geologic source location of cultural artifacts. Mineralogy combined with
chemical analysis provides major element ranges for comparison. Overlapping ranges of the
cations Cu, Al, and Fe involved in the solid solution series of the minerals turquoise,
chalcosiderite, and planerite show promise for providing chemical signatures of turquoise
sources. Preliminary results show that samples from an Ancestral Puebloan archaeological site
near Thoreau, New Mexico have more compositional similarity to a prehistoric mine at Hachita
than geographically closer mines in the Cerrillos mining district.

INDEX WORDS: turquoise, chalcosiderite, planerite, petrography, electron microprobe, X-
ray diffraction, prehistoric mining, Ancestral Puebloan, Hachita, Cerrillos,
New Mexico
MINERALOGICAL AND COMPOSITIONAL ANALYSIS OF TURQUOISE ARTIFACTS
LINKED TO PREHISTORIC MINES IN NEW MEXICO, USA

by

CYNTHIA HOTUJEC
BA Anthropology, Georgia State University, 2003

A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment
of the Requirements for the Degree

MASTER OF SCIENCE

ATHENS, GEORGIA
2011
© 2011
Cynthia Hotujec
All Rights Reserved
MINERALOGICAL AND COMPOSITIONAL ANALYSIS OF TURQUOISE ARTIFACTS
LINKED TO PREHISTORIC MINES IN NEW MEXICO, USA

by

CYNTHIA HOTUJEC

Major Professor: Samuel E. Swanson
Committee: Douglas Crowe
Ervan G. Garrison

Electronic Version Approved:

Maureen Grasso
Dean of the Graduate School
The University of Georgia
May 2011
iv

TABLE OF CONTENTS
Page
LIST OF TABLES ......................................................................................................................... vi
LIST OF FIGURES ....................................................................................................................... vii
CHAPTER
1 Introduction .................................................................................................................. 1
Prehistoric Mining of Cultural Turquoise in the American Southwest .................. 1
Mineralogy ............................................................................................................. 3
Previous Turquoise Source Studies ......................................................................... 6
Justification for Study ............................................................................................ 11
2 Archaeological Setting of Turquoise Artifacts ........................................................... 14
Prehistory of the American Southwest ................................................................. 14
Blue J Project ........................................................................................................ 17
3 Geologic Setting of Prehistoric Turquoise Mines ...................................................... 20
Occurrence ............................................................................................................ 20
Copper Porphyry Deposits ................................................................................... 20
Hydrothermal Fluids ............................................................................................. 22
Alteration Zones ................................................................................................... 23
Weathering ........................................................................................................... 26
Geology of Mines Analyzed ................................................................................. 30
4 Methodology ............................................................................................................... 38
v
Sample Numbering ............................................................................................... 38
Sample Collection ................................................................................................ 39
Sample Color ........................................................................................................ 42
Sample Preparation ............................................................................................... 42
Petrography ........................................................................................................... 43
X-ray Diffraction .................................................................................................. 44
Electron Microprobe Analysis .............................................................................. 44
Data Processing .................................................................................................... 46
5 Results ........................................................................................................................ 48
Hachita .................................................................................................................. 48
Red Hill ................................................................................................................ 65
Chalchihuitl .......................................................................................................... 74
Tiffany .................................................................................................................. 79
Blue J Artifacts ..................................................................................................... 82
Data Analysis ........................................................................................................ 84
6 Conclusions ................................................................................................................ 97
REFERENCES ............................................................................................................................ 100
APPENDICES
A Artifact Photographs ................................................................................................ 107
B Mine Sample Photographs ....................................................................................... 117
C Color ........................................................................................................................ 146
D Sample Inventory ..................................................................................................... 147
E Petrography .............................................................................................................. 152
vi
F EMPA of Turquoise Samples ................................................................................... 171
G EMPA of Homogeneous Turquoise Minerals ......................................................... 295
H X-ray Diffraction ..................................................................................................... 311
vii

LIST OF TABLES
Page
Table 1.1: Theoretical turquoise endmember composition determined by stoichiometry. ............. 3
Table 4.1: Site and dates of turquoise artifacts .............................................................................. 40
Table 4.2: Turquoise substandard analyses results, means, and standard deviations .................... 45
Table 4.3: Criteria for inclusion of individual analyses in averages of turquoise material ........... 45
Table 4.4: Representative sample of typical minimum detection limits ....................................... 46
Table 5.1 Major cation range, average, and standard deviation for each Hachita sample ............ 58
Table 5.2: Individual analyses for sample TM127 ........................................................................ 59
Table 5.3: Major cation range, average, and standard deviation for Red Hill samples ................. 73
Table 5.4: Major cation range, average, and standard deviation for Chalchihuitl samples ........... 75
Table 5.5: Major cation range, average, and standard deviation for Tiffany samples .................. 80
Table 5.6: Major cation range, average, and standard deviation for Blue J samples .................... 85
Table 5.7: Pair wise comparisons of p-values for copper, iron, and aluminum cations ................ 87
Table 5.8: Mine comparisons by artifact ...................................................................................... 94
viii

LIST OF FIGURES
Page
Figure 1.1: Ternary diagram of turquoise group endmembers and solid solution series ................ 5
Figure 2.1: Map of places mentioned in text. ................................................................................ 16
Figure 3.1: Porphyry copper belts of the world ............................................................................. 21
Figure 3.2: Location of hydrothermal veins .................................................................................. 22
Figure 3.3: Idealized results of the interaction of hypogene and supergene alteration ................. 23
Figure 3.4: Generalized model of porphyry copper formation ...................................................... 24
Figure 3.5: Alteration and mineralization zones of copper porphyries ......................................... 25
Figure 3.6: Locations Sampled in New Mexico ............................................................................ 30
Figure 3.7: Location of the Red Hill turquoise mine Burro Mtns., NM ........................................ 31
Figure 3.8: Location of Azure turquoise mine, Little Hatchet Mtns., NM .................................... 32
Figure 3.9: Intrusives and extrusives of the Cerrillos Hills ........................................................... 34
Figure 3.10 Major turquoise deposits of the Cerrillos Mining District ......................................... 35
Figure 4.1: Locations of archaeological sites and prehistoric turquoise mines ............................. 40
Figure 5.1: Weathered Hachita turquoise ...................................................................................... 48
Figure 5.2: Turquoise veins at Hachita .......................................................................................... 49
Figure 5.3: Spherulitic turquoise in sample TM127 ...................................................................... 50
Figure 5.4: Sample TM102 vein-like network structure ............................................................... 50
Figure 5.5: Hachita sample TM115 ............................................................................................... 51
Figure 5.6: TM118 silica border along turquoise vein and red inclusion ..................................... 52
ix
Figure 5.7: Sample TM115 fractured and altered phenocrysts in host rock .................................. 53
Figure 5.8: Sample TM102 iron stains near host rock .................................................................. 53
Figure 5.9: Phenocrysts in Hachita host rock ................................................................................ 54
Figure 5.10: Analysis points targeted areas void of host rock, inclusions and alteration ............. 54
Figure 5.11: Hachita sample averages plotted with turquoise minerals ........................................ 56
Figure 5.12: TM114 spherules ...................................................................................................... 57
Figure 5.13: TM127 spherules with iron-rich centers surrounded by aluminum silicates ............ 59
Figure 5.14: Experimental X-ray diffraction patterns of samples ................................................. 62
Figure 5.15: Samples from Red Hill mine, White Signal mining district, New Mexico .............. 66
Figure 5.16: Rounded aggregates in Red Hill sample RH13 ........................................................ 67
Figure 5.17: Sample RH10 ............................................................................................................ 67
Figure 5.18: Two types of sericite intergrowth ............................................................................. 68
Figure 5.19: Iron oxide in sample RH13 with opaque inclusions ................................................. 68
Figure 5.20: Alteration of biotite and chlorite of host rock in sample RH19 ................................ 69
Figure 5.21: Sample RH9 .............................................................................................................. 69
Figure 5.22: Red Hill sample averages plotted with turquoise minerals ....................................... 71
Figure 5.23: Red Hill and Hachita homogeneous averages plotted with high-Fe analyses .......... 72
Figure 5.24: RH17 veinlets with lower Cu, Al, P and higher Fe than surrounding material ........ 72
Figure 5.25: Sample CH23 exhibits color variability at the sample scale ..................................... 74
Figure 5.26: Chalchihuitl sample averages plotted with turquoise minerals ................................. 76
Figure 5.27: Chalchihuitl sample textures ..................................................................................... 77
Figure 5.28: Textural variation in Chalchihuitl samples ............................................................... 78
Figure 5.29: Spherulitic texture of sample CH34 and dense inclusions of sample CH23 ............ 78