Abstract ........................................................ 1
Introduction .................................................... 1
Physical Setting ................................................ 2
Geographic and Physiographic Features ........................ 2
Climate and Vegetation ....................................... 2
General Geology ................................................. 4
Mining History .................................................. 6
General Hydrology ............................................... 6
Surface Water ................................................ 6
Ground Water and Aqueous Geochemistry ........................ 6
Methods and Previous Work ....................................... 7
Brittle Structures of the Questa Caldera ........................ 8
Joint Networks ............................................... 8
Faults, Fault Zones, and Fault-Related Fracture Networks ........ 8
Low-Angle Structures ........................................ 13
High-Angle Composite Deformation Zones ...................... 15
High-Angle Distributed Deformation Zones .................... 18
Other Potential Structural and Hydrogeologic Heterogeneities
in the Questa Caldera ....................................... 22
The Caldera Margin and Ground-Water Flow .................... 22
Stockwork and Other Vein Systems ............................ 22
Lithologic Contacts ......................................... 22
The Range-Front Fault Zone .................................. 23
Faults in Surficial Deposits ................................ 23
Insights from Estimation of Bedrock, Caldera Margin, and
High-Angle Fault-Zone Permeability Structure ................ 23
Introduction to Computations ................................ 23
Computational Results for the Bedrock ....................... 26
Computation and Results for the Caldera Margin and High-
Angle Small Faults .......................................... 28
Summary and Discussion of Potential Structural Controls on
Bedrock Ground-Water Flow ...................................... 31
Acknowledgments ................................................ 35
References Cited ............................................... 35
Figures
1 Location and topographic map of the study area, showing
alteration scars (yellow), debris fans (blue), known ore
bodies (red), the mine site (pink), and the open pit
(black dashed line) .......................................... 3
2 Simplified geologic map of the southern portion of the
Questa caldera in the vicinity of Red River, New Mexico ...... 4
3 Southwest section of the simplified geologic map of the
Questa caldera shown in figure 2 ............................. 9
4-7. Photographs:
4 View looking south at open joints with simple orthogonal
orientations at the Tsed locality a few meters above the
main Red River channel ...................................... 10
5 Oblique view of complex orthogonal open joints at the
Amalia Narrows locality at the edge of the main stream
channel ..................................................... 10
6 View looking down on joints with conjugate geometry at
the Small Scar locality ..................................... 11
7 Example of a high-intensity, highly interconnected joint
network found in the Pit Ore Body locality .................. 11
8 Conceptual diagram of distinctive fault-zone architectural
styles found in nature ...................................... 13
9 Geologic map draped onto a 30-meter digital elevation
model with no vertical exaggeration and a 100-foot contour
interval .................................................... 14
10-20. Photographs:
10 Low-angle fault zone looking approximately west, showing
Tertiary rhyolite and boulder conglomerate in the upper
plate and Precambrian granite in the lower plate ............ 15
11 Fault damage zone of the low-angle fault
zone......................................................... 16
12 Closeup view of phacoidally cleaved, white, red, and
black, clay-rich fault gouge in the low-angle fault-zone
core......................................................... 16
13 Closeup view of silicified, polished, and striated slip
surfaces that mark the contact of the upper and lower
plates of the low-angle fault zone .......................... 17
14 View looking south of the high-angle fault zone that
intersects the low-angle fault zone at the lower left-hand
corner of photograph ........................................ 17
15 View looking north at the fault core of the high-angle
fault zone................................................... 19
16 Manganocrete deposit (iron and manganese oxide-cemented
alluvial and colluvial materials) at the base of the Cabin
Springs cliffs on the north bank of the Red River ........... 19
17 View looking north at the Cabin Springs cliff rhyolite
dike that strikes parallel to the plane of the photograph
and is cut by open and relatively small extensional
faults ...................................................... 20
18 View looking north at small faults, fault-related fracture
networks, and near-orthogonal joint sets in the Bear
Canyon pluton at the mountain front and the west end of
the Red River Valley ........................................ 20
19 View looking north at the fault core of a small fault in
the Cabin Springs cliffs .................................... 21
20 Small extensional fault and primary slip surface in
the lower pit ore body showing "moly paint" and iron oxide
staining that is probably related to recent seepage, and
open fractures in the footwall damage zone .................. 21
21 Segment of a geologic cross section from the geologic map
of the Latir volcanic field including the Questa caldera .... 22
22 Diagram showing two-dimensional, cross-sectional ground-
water flow net for a region with high gradients and an
isotropic, homogeneous bedrock aquifer at the bottom of
which there is a no-flow boundary............................ 23
23 Schematic diagram showing an average topographic profile
from the north divide of the Red River watershed to
the river, average potential topographic head gradients
for varying depths to water at the divide, and the
geometry and parameters used ................................ 26
24 Pseudo three-dimensional geologic and topographic map
draped on a 30-meter digital elevation model with no
vertical exaggeration showing the model setup for
computations of hydraulic conductivity for the bedrock
aquifer system on the north divide .......................... 28
25 Plot of computed hydraulic conductivity (K) values
relative to depth of cross-sectional areas for estimated
gradients and values of estimated bedrock discharge to
the Red River alluvial aquifer .............................. 29
26 Pseudo three-dimensional geologic and topographic map
draped on a 30-meter digital elevation model with no
vertical exaggeration ....................................... 30
27 Plot of computed К values relative to depth of fault
damage zones for gradients and values of estimated
discharge to the Red River alluvial aquifer system .......... 31
28 Combined plot (plots 25 and 27) of computed К values
relative to geological feature cross-sectional area depth
for the bedrock alone and for fault damage or distributed
deformation zones ........................................... 32
29 Fifteen-meter resolution, natural-color satellite image
draped on a USGS digital elevation model .................... 33
Tables
1 Joint intensity data ......................................... 9
2 Fault-related damage zone fracture intensity data ........... 12
3 Small fault intensity data .................................. 18
4 Reported bedrock hydraulic data for the region around the
Questa mine and the USGS Straight Creek research site ....... 24
5 Input data and summary statistics for computed and
reported bedrock and fault zone hydraulic properties ........ 27
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