Regional geology in the Opodepe mining area, Sonora, Mexico
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Authors Ramírez Muñoz, José
Publisher The University of Arizona.
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Link to Item http://hdl.handle.net/10150/555133 REGIONAL GEOLOGY IN THE OPODEPE
MINING AREA," SONORA, MEXICO
by
Jose Ramirez Munoz
A Thesis Submitted to the Faculty of the
DEPARTMENT OF MINING AND GEOLOGICAL ENGINEERING
In Partial Fulfillment of the Requirements For the Degree of
MASTER OF SCIENCE WITH A MAJOR IN GEOLOGICAL ENGINEERING
In the Graduate College
THE UNIVERSITY OF ARIZONA
1 9 7 9 STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfill ment of requirements for an advanced degree at The Univer sity of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable without special permission, provided that accurate acknowl edgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole of in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the inter ests of scholarship. In all other instances, however, per mission must be obtained from the author.
SIGNED: /27-
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
z y , / ? 7 ‘r WILLIAM C. PETERS £ / Data Professor of Mining and Geological Engineering ACKNOWLEDGMENTS
The work on this program was done under the direc tion and sponsorship of AMAX Exploration, Inc. and Minera
Opodepe, SRL de CV. Dr. Willem Lodder and Mr. Feliciano
Leon of AMAX exploration, Inc. directly supervised my field work on the property, and Dr. C P . Miller of AMAX
Exploration, Inc. provided overall supervision and direc tion. Both AMAX Exploration, Inc. and Minera Opodepe, SRL de CV provided financial support for both field work and chemical analyses. Mr. Daniel Valenzuela of AMAX Explora
tion in Tucson, Arizona, assisted greatly in map prepara
tion and illustration.
I wish to express my appreciation to these compa
nies and to the involved geologists for their support and
encouragement during the course of this work and for per mission to use company data in this thesis.
I want to thank Dr. William C. Peters, my thesis
director, and Dr. Deverle P, Harris for their valuable
suggestions and encouragement. I also wish to thank Dr.
Charles E. Glass, who served on my thesis committee. In
addition I want to thank The University of Arizona, spon
sor of the computer time used for the trend surface
analysis.
iii iv
I wish to thank my wife and children for their help and understanding during my stay in Tucson. I will be always in debt to my father and to all my family for
their support, advice, and encouragement given throughout my studies. iv
I wish to thank my wife and children for their help and understanding during my stay in Tucson. I will be always in debt to my father and to all my family for
their support, advice, and encouragement given throughout my studies. TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS...... vii
ABSTRACT...... ix
INTRODUCTION...... 1
Purpose...... H H c o c o i n Method of Study...... Location ...... Topography and Climate . History and Previous Work
REGIONAL GEOLOGY ...... 7
Geomorphology...... 7 Sierra Madre Occidental Province ...... 9 Sonoran Desert Province...... 10 Coastal Plains of Sinaloa Province ...... 11 Stratigraphy ...... 11 Precambrian...... 11 Paleozoic...... 13 Mesozoic...... 15 Cenozoic...... 18 Structural Geology ...... 19
GEOLOGY OF THE OPODEPE MINING A R E A ...... 23
Geomorphology...... 23 Stratigraphy ...... 25 Sedimentary Rocks...... 26 Igneous Rocks...... 28 Metamorphic Rocks...... 32 Structural Geology ...... 36 Folding...... 36 Fractures...... 39 F a u l t s ...... 40 Foliation...... 42 Dikes...... 43 Breccias...... 43 Mineralization ...... 44
v vi
TABLE OF CONTENTS— Continued
Page
EXPLORATION TECHNIQUES USED IN THE OPODEPE MINING AREA...... 45
Photogeology ...... 45 Photogeologic Description of the Units . . . 46 Summary...... 57 Lineament Analysis ...... 60 Geochemical Trend Analysis ...... 62 Geostatistics...... 62 Stream Sediment Survey ...... 68 Rock Chip S u r v e y ...... 77 Comparison of the Different Surveys...... 86
CONCLUSIONS AND RECOMMENDATIONS...... 88
APPENDIX: STATISTICAL CALCULATIONS FOR THE TREND SURFACE MAPS...... 91
REFERENCES...... 96 LIST OF ILLUSTRATIONS
Figure Page
1. Location map of Opodepe, Sonora, Mexico...... In pocket
2. Location map of study area...... 4
3. Regional geologic map, Opodepe mining area, Sonora, Mexico (2 sheets)...... In pocket
4. Geomorphic Provinces in the State of S o n o r a ...... 7
5. Paleozoic paleogeograph and isopach m a p ...... 14
6. Structural map of Sonora, Mexico...... 20
7. Geologic cross section A-A*, Opodepe mining area, Sonora, Mexico ...... In pocket
8. Geologic cross section B-B1, Opodepe mining area, Sonora, Mexico ...... In pocket
9. Geologic cross section C-C1, Opodepe mining area, Sonora, Mexico ...... In pocket
10. Photolineament map, Opodepe mining area, Sonora,Mexico ...... In pocket
11. Lineament histogram...... 61
12. Geochemical surveys, Opodepe mining area, Sonora, Mexico...... In pocket
13. Location map of the sampled cells, Opodepe mining area, Sonora, Mexico . . . In pocket
14. Molybdenum trend surface map from the stream sediment survey...... 69
15. Molybdenum residuals from the stream sediment survey ...... 70
vii viii
LIST OF ILLUSTRATIONS— Continued
Figure Page 16. Plot of molybdenum values from the stream sediment s u r v e y ...... -72
17. Copper trend surface map from the stream sediment s u r v e y ...... <73
18. Copper residuals from the stream sediment survey ...... 75
19. Plot of copper values from the stream sediment s u r v e y ...... 7G
20. Molybdenum trend surface map from the rock chip s u r v e y ...... 79 21. Molybdenum residuals from the rock chip s u r v e y ...... 80
22. Plot of molybdenum values from the rock chip s u r v e y ...... 81
23. Copper trend surface map from the rock chip s u r v e y ...... g3
24. Copper residuals from the rock chip s u r v e y ...... 34
25. Plot of copper values from the rock chip survey 85 viii
LIST OF ILLUSTRATIONS— Continued
Figure Page
16. Plot of molybdenum values from the stream sediment survey ...... 72
17. Copper trend surface map from the stream sediment survey ...... 73
18. Copper residuals from the stream sediment survey ...... 75
19. Plot of copper values from the stream sediment survey ...... 76
20. Molybdenum trend surface map from the rock chip survey ...... 79
21. Molybdenum residuals from the rock chip s u r v e y ...... 80
22. Plot of molybdenum values from the rock chip s u r v e y ...... 81
23. Copper trend surface map from the rock chip survey ...... 83
24. Copper residuals from the rock chip survey ...... 84
25. Plot of copper values from the rock chip survey 85 ABSTRACT
The Opodepe mining area is located northeast of
Hermosillo, Sonora, Mexico and is currently controlled by
Cia. Minera Opodepe, SRL de CV. The area became of inter est after a review of known data and a field evaluation of alteration and mineralization.
The author conducted a reconnaissance geologic and geochemical program under the direction and sponsor ship of AMAX Exploration, Inc. and Cia. Minera Opodepe.
The available aerial photographs were most useful during the field work.
The area of study is composed of a mixture of gneisses and mafic Precambrian rocks, which are overlain by a series of steeply dipping quartzite beds. During the Laramide orogeny, all these rocks were strongly deformed and intruded by several plutons. Later, during the Basin and Range orogeny, the thesis area was again strongly faulted.
The geochemical program consisted of a reconnais sance stream sediment survey and a detail rock chip survey done on Creston ridge. The trend surface map from the stream sediment survey outlines Creston ridge and in a general way correlates well with the rock chip trend sur face map.
ix INTRODUCTION \ The thesis area is a part of the Opodepe mining area, located in the vicinity of Opodepe, Sonora, Mexico
(Fig. 1, in pocket).
Purpose
Cerro Creston is a strongly altered and moderately mineralized mountain close to the town of Opodepe. Com- pania Minera Opodepe conducted an exploration program at
Cerro Creston with encouraging results; this led to a regional exploration program designed to evaluate part of the Opodepe mining area.
Work for this thesis was conducted under the direction and sponsorship of AMAX Exploration, Inc. and
Cia. Minera Opodepe. These companies provided funds for field and office work and for all the chemical analyses.
Method of Study
Minera Opodepe geologists mapped at and around
Cerro Creston covering an irregular surface of approxi mately 20 square kilometers. Later, from July to October,
1975, the author did a regional reconnaissance around the area mapped by the Minera Opodepe staff. Using the same symbols, the mapping was extended outward from the Cerro
Creston area and the field work was done as a combination
1 2 of field mapping and photogeological interpretation. For this study, black-and-white and color aerial photographs were obtained at an approximate scale of 1:10,000. The aerial photographs were used as a base for field mapping and all the information was placed on acetate overlays.
Later an uncontrolled mosaic was available to put together all the information obtained from the field; the photo mosaic was at approximately the same scale as the photo graphs. During the field work rock samples were collected for thin sections for petrographic study.
Results of a geochemical program carried out in the Opodepe mining area were made available by Cia. Minera
Opodepe, and these results were computer-coded for the
trend analysis described in the chapter on exploration
techniques used in the Opodepe mining area. The above
program included a rock chip survey carried out in the
Cerro Creston area plus a stream sediment survey conducted
in and around the area of study.
In 1974 a private company (IFEX) was contracted
by Cia. Minera Opodepe to make a topographic map of the
Cerro Creston area from aerial photographs. IFEX assigned
for convenience the coordinates 10,000 E and 10,000 N and
1000 m elevation for the top of Cerro Creston, which was
used as the main control point. Later Detenal (an agency
of the Mexican government) issued topographic maps at a 3 scale 1:50/000 for the whole country. Detenal used the
Universal Transversal Mercator coordinate system for their maps, and in this paper both sets of coordinates were used.
Location
The town of Opodepe lies on the eastern edge of the study area, which covers an irregular surface of 2 approximately 100 km (Fig. 2). The Mercator coordinates for this area are X = 524,000 to X = 537,000 and
Y = 3,303,000 to 3,312,000.
Opodepe is located approximately 100 airline km
N. 21° E. of Hermosillo and approximately 160 airline km
S. 11° E. of Nogales, Sonora, Mexico. The town is 673 m above sea level, with a geographical location at lat
29°55140" N. and long 110°37,35" W. (Fig. 1, in pocket).
Opodepe can be reached by traveling 65 km north from
Hermosillo along the main highway then turning east at
El Oasis to travel 8 km to Garbo, and finally 67 km to
the northeast on a well-graded dirt road.
Topography and Climate
Topographic relief in the area of study is about
500 m with the highest point being 1,200 m above sea level.
Most slopes to the west of the San Miguel River are cov
ered by colluvium, and 80 percent of the area to the east
of the river is covered by alluvium; this limits the
amount of outcrop to 30 or 40 percent of the total area. 4
SAN mCAROO
SAN JERO NIM O #
S TA. MARGARITA
/ ; ^ EL S O C O R R O ^ )
TRES ALANOS
29 4 5
Dirt roods- mom ond access GRAPHIC SCALE Mine I >250,000 Area mopped by Cio. Mmero Opodepe 0 1 5 10 Km Areo of Study N
Fig. 2. Location map of study area 5
Two general topographic trends can be distinguished. One trend, N. 70° E. to N. 80° E., is quite obvious on the geologic map (Fig. 3, 2 sheets, in pocket). This trend is controlled by structure and rock type. The other trend,
N. 40° W., is less apparent on the geologic map. It is also controlled by rock type and structure.
The climate in this region is very characteristic
of semidesert areas, with high temperatures and cloud bursts common in the summer and cold windy winters accom
panied by occasional rains and some snow in the high
mountains.
History and Previous Work
Most of the mining activity in the area of study
has consisted of small pits and small adits from which
there was probably very little or no production. Although
there were three small mines that produced gold, silver,
lead, and zinc, there is no record of their production and
according to local people very little ore was mined.
There are two adits of approximately 100 m each at Cerro
Creston; both were driven for exploration purposes.
Three fairly large mines or mining areas fall
inside a circle with a 10-km radius having Cerro Creston
as the center. One of these mining areas comprising a
series of shafts and tunnels is El Socorro; it is approxi
mately 8 km west of Cerro Creston. The orebody at El 6
Socorro appears to be completely mined out. According to local people, the workings in the other two mines, San
Jeronimo and San Ricardo, are still in ore but the adits have caved and the shafts are flooded. All three mines produced ore from rich gold and silver veins, but there are no production records available. The last of these mines stopped producing in 1940.
Several companies have done geologic reconnaissance in the Cerro Creston area; some looked for copper; others explored for molybdenum. At the time, the results were not very encouraging. In 1974 Cia. Minera Opodepe (an
AMAX Exploration Inc. and Servicios Industriales Penoles
SC. joint venture) started an exploration program includ ing detailed mapping and some drilling with encouraging results. REGIONAL GEOLOGY
Although the state of Sonora has not been studied in complete detail, the work done by geologists gives a fair understanding of the geology and the main sequence of events that have taken place through geologic time. A brief description of the regional geology will be given so the reader can relate it to local geologic conditions.
Whenever a reference in this thesis is made to an area close to Opodepe, it will be described in relation to the state topographic and geologic maps because there is no specific geologic data available close to the thesis area.
Geomorphology
King (1939) has given an excellent description of the geomorphology of central Sonora and his observations apply very well to the whole state. In the same year,
Imlay (1939) added some observations to the geomorphology of northeastern Sonora. Later, Alverez (1966) made a good summary and reinterpretation of the available information and proposed three geomorphic provences for Sonora: the
Sierra Madre Occidental, the Sonoran Desert, and the
Coastal Plains of Sinaloa (Fig. 4).
7 8
,Son Lu»s Rio Cotorodo
Pto. PtMosco0- CHIHUAHUA
I . SONORAN DESERT PROVINCE
E . SIERRA MADRE OCCIDENTAL PROVINCE A.- Basin and Range Section M u 0 ♦ 0 b O 0 /o B- Barranca Section EtcnoiooX^*, IE. COASTAL PLAINS OF SINALOA PROVINCE
100 150 250 km
Fig. 4. Geomorphic provinces in the State of Sonora 9
Sierra Madre Occidental Province
The Sierra Madre Occidental is an elongate north- south mountainous belt 1,200km long and 250 km wide, which covers part of Sonora and extends into Chihuahua. Because of the changes in topography and land form, the province has been subdivided into three subprovinces or sections:
Plateau, Barranca, and Basin and Range (Alvarez, 1966).
Plateau Section. This section lies entirely in
Chihuahua and is characterized by a gently rolling surface carved into volcanic rocks, with mountains separated by broad valleys. It has a mature topography, and the vol canic rocks are mostly Tertiary rhyolites underlain by folded Mesozoic rocks.
Barranca Section. The Barranca section, west of the Plateau section, is named from the deep gorges (bar rancas) that the rivers have cut through the volcanic rocks. Some of these barrancas are 2,000 m deep. The
change to a youthful topography from the mature topography of the Plateau section is well marked by a 300-m escarp ment. Structure has had little effect on the topography
and drainage lines. Volcanics with some interlayered
sedimentary rocks provide most of the outcrops in this
subprovince; there are also a few areas in which intrusive
rocks crop out (King, 1939). 10
The Basin and Range Section. This section, which contains the thesis area, is parallel to and west of the
Barranca subprovince; it is approximately 150 km wide at the Mexico-U.S. border and 30 km wide at the Sonora-
Sinaloa border. The main physiographic characteristic is a series of parallel ranges and intermountain valleys that form horsts and grabens with a N. 10° W. trend. The moun tain ranges have a more abrupt topography and sharper con tact with the adjacent valleys to the east and have a larger and better development of pediments to the west; this change in topography is noticeable along the San
Miguel River and the Sonora River. In this subprovince the geomorphic features are very closely related to the underlain rocks (Imlay, 1939). The structure consists mostly of normal faults, with some thrust faults reported.
The outcropping rocks range in age from Precambrian to
Holocene.
Sonoran Desert Province
The Sonoran province covers from 40 to 50 percent of the state and lies west of the Sierra Madre Occidental.
It is predominantly a large plain with steep inselbergs having no apparent orientation. It has a mature topogra phy. 11
Coastal Plains of Sinaloa Province
The Coastal Plains of Sinaloa province lies south of the 28th parallel and the Sonoran Desert province. King
(1939) describes this province as an alluvial plain formed
by the coalescing deltas of the Yaqui, Mayo, and Fuerte
Rivers.
Stratigraphy
Several stratigraphic sections in Sonora have been
studied in detail. The description of the different for mations has been the basis for correlations with strati
graphic columns in southern Arizona and western Chihuahua.
The understanding of each section and the correlations
between them have been very useful in trying to understand
the regional geology pertaining to the thesis area.
Precambrian
Precambrian stratigraphy has been difficult to
study, partially because of the lack of fossils and par
tially because of the strong deformation that the rocks
have been subjected to. The Precambrian has been divided
into older and younger categories on the evidence of a
great unconformity that separates the two. The older
rocks are generally more strongly metamorposed. The older
Precambrian rocks consist of metasediments, metavolcanics,
schists, gneisses, shales, limestones, quartzites, and
dolomites. They crop out at Altar (Cooper and Arellano, 12
1946) , Bamuri (Damon, 1968), Cabullona (Taliafierro, 1933),
La Morita (Taliafierro, 1933), Sierra de Los Ajos, and in an area northeast of Opodepe.
The age of the metamorphic event is considered to be between 1600-1700 m.y. B.P. (Fries, 1962). The Altar schist has a radiometric age of 1680 m.y. B.P. (Damon,
Livingston, and Giletti, 1962). Damon (1968) considers that the Arizona revolution (1630-1760 m.y. B.P.) rather than the Mazatzal revolution is responsible for the meta morphism; the Mazatzal revolution is believed by Damon to have taken place between 1370 and 1450 m.y. ago. The only intrusive rocks that might be related to the Mazatzal event are the Aibo Granite (Damon, 1968), a 1440 m.y.-old granite at Cananea (Anderson and Silver, 1973), and a quartz monzonite in the San Antonio Mountains (Ramirez R., 1965).
The younger Precambrian rocks, resting unconforma- bly on older Precambrian, are represented by a sedimentary
sequence of quartzites, shales, limestones, and dolomites with some low-grade phyllites and metaconglomerates.
These rocks crop out at Caborca (Cooper and Arellano,
1946) , Sonoita (Damon, 1968), and Magdalena (Salas, 1970).
The deposition of Precambrian sediments was restricted to
the northern part of the state with the greatest accumula
tion around Caborca. 13
Paleozoic
During this era, a shallow elongate north-south trough (Sonoran basin) developed and filled rapidly in the northwestern part of the state (Solano R., 1975). The
Sonoran basin continued receiving sediments during the
Paleozoic era. There is no record of Paleozoic intrusive rocks, but there were probably some epeirogenic movements,
as indicated by a successive change in the Paleozoic
shoreline (Fig. 5).
In Cambrian time the seas covered the northern
part of the state; the sedimentary rock sequence consists
of limestones, shales, and quartzites. At Altar (Cooper
and Arellano, 1946), the Paleozoic sedimentary sequence is
underlain by an unconformity and by the Precambrian base
ment; at Cananea the basement is unknown (Mulchay and
Velasco, 1954). There are small remnants of Cambrian
quartzites in the Sierra de San Antonio (Ramirez R., 1965).
Later in the Ordovician and Silurian periods, the seas
were restricted to the western part of Sonora, and the
only outcrops known are of Ordovician limestones at La
Casita and Sierra del Cobachi (King, 1939).
During Devonian time the seas started to move east
ward; 285 m of Lower Devonian limestones and dolomites
crop out in the Altar region (Cooper and Arellano, 1946)
and at Cananea (Maldonado, 1954). In Late Devonian time
the seas covered the eastern part of Sonora. Limestones 14
Possible moxlmun southern extent of Paleozoic seas
a fte r Solano Rico. 3.. 1975
Fig. 5. Paleozoic paleogeography and isopach map 15 and shales of this age crop out at Cabullona (Alvarez,
1966) . Later, in Mississippian and Pennsylvanian time, the same geologic conditions continued and the rocks associated with these periods are mostly limestones with minor inter- bedded layers of shales. They crop out at Altar (Alvarez,
1966) , Cabullona (Taliafierro, 1933), El Tigre (Imlay,
1939) , and Cananea (Mulchay and Velasco, 1954).
Near the end of the Paleozoic, during Permiam time, the seas continued transgressing to the south until they covered more than two-thirds of the state. In this period, sandstones, shales, and limestones were deposited with apparent greater thickness in the northeast corner of
Sonora. The thickness of the sedimentary sequence is
160 m at Altar (Cooper and Arellano, 1946), 550 m in
Hermosillo (King, 1939), and 1,800 m in the El Tigre area
(Imlay, 1939). Paleozoic sedimentary rocks have been mapped in small areas northwest of Opodepe, but they have not been differentiated.
Mesozoic
Mesozoic rocks are widely exposed throughout the state, but they are most abundant in the Basin and Range section. Sonora continued to be fairly stable except for epeirogenic movements until Cretaceous time, when magmatic activity started. 16
Triassic-Jurassic. There was an uplift in Late
Permian and Early Triassic time and there is no strati graphic record of this period of time. Late in Late Trias sic time an elongate northwestern-southeastern geosynclinal basin developed. The sedimentary sequence, deposited until
Early Jurassic, was named by Durable (1900) as the Barranca formation? he and King (1939) described this formation in detail. East of meridian 110° W. the sedimentary sequence consists mostly of quartzites with occasional thin shale beds. One of the main features in this sequence is at least one thin coal bed and a graphite bed. Between merid ians 110° W. and 111° w. there are more shale beds, and thin limestone beds start to appear west of meridian 111°
W. There, the sequence has more limestones than shales or quartzites, and the coal and graphite beds disappear. A
sedimentary sequence of sandstones, shales, and limestones correlative to the Barranca formation crops out west of the village of Rayon. Vasquez Perez (1975) reports that vol canic rocks of this age were mapped and dated in northern
Sonora between meridians 110° W. and 111° W.
Cretaceous. In Late Jurassic and Early Cretaceous
time, the Occidental geanticline was formed west of the
Barranca Basin (Eardley, 1962). This activity kept the
land above sea level until Albian time when the seas again
flooded this part of Sonora. During this time, large 17 quantities of sediments and volcanic flows were deposited unconformably on earlier Mesozoic rocks. The ratio of volcanic rocks to sedimentary rocks increases toward the west, so that in places there are only volcanic rocks present. Andesitic flows are more abundant with only small rhyolitic flows at the top of the sequence. Limestones, shales, and sandstones outcrop in Sahuaripa (King, 1939).
Later during the Middle to Late Cretaceous period the western part of Sonora was uplifted, which probably marked the beginning of the Laramide orogeny, and there was deposition only in the Cabullona area (Taliafierro, 1933).
Clastic sediments interlayered with minor volcanic flows are present in the northeastern part of the state.
The Laramide orogeny occurred in Sonora between
52-72 m.y. ago, as determined by isotopic age dates done in several intrusive rocks by Damon and Mauger (1966) and
Livingston (1973). There is also stratigraphic evidence of Laramide orogeny in several places, as in the El Tigre area where a granitic mass intrudes Cretaceous sediments and does not intrude Tertiary volcanics. During this time most of the large granitic batholithic masses were emplaced, accompanied by uplift and strong deformation of older rocks 18
Cenozoic
This era was characterized by great tectonic activity and by the deposition of volcanic flows and clas tic rocks. The Laramide orogeny continued, with granitic intrusions and andesitic flows which probably stopped in the early Eocene. During Eocene time there was a period of nondeposition and erosion. In late Eocene time a second volcanic pulse started, which probably had its maximum intensity in Oligocene or Miocene time and was associated with minor intrusions (Wisser, 1966). This volcanic sequence consists mostly of rhyolite and tuff flows; the flows rest unconformably on older Tertiary rocks. The whole Tertiary sequence is well exposed in the Barranca and Plateau sections.
The Basin and Range orogeny is later than the
Laramide orogeny and is probably contemporaneous with mid-
Tertiary volcanism. This younger orogeny produced elongate north-northwesterly trending parallel zones of horsts and grabens bordered by normal faults.
The Baucarit formation (Pliocene?) probably accumu lated in closed basins, mostly in the Basin and Range sub province, and it is well exposed in the grabens. Durable
(1900) describes this formation as extremely even-bedded
sands, clays, and conglomerates, in places with a lower basaltic member 21 m.y. old (Vasquez, 1975). 19
During the Quarternary period large quantities of loose material have accumulated over the state, as seen on cuestas, pediments, river banks, and river channels. One of the best examples of recent sedimentation is on the
Coastal Plain of Sinaloa. King (1939) reports basaltic flows probably of Pleistocene age that are younger than the Baucarit formation.
Structural Geology
The structural trends resulting from the Basin and
Range (mid-Tertiary) orogeny partially obliterate older structural trends and make it difficult to study the structural history of the state. From the regional and detailed geologic studies done in Sonora, it can be con cluded that the state has gone through three orogenic events and several epeirogenic events. The predominant structural trends in Sonora are N. 0°-10o W . , northwest., and north-northeast. An east-northeast structural trend has been well recorded, but it is not noticeable in the
state structural map (Fig. 6).
It has been very well determined that an east- northeast structural trend was caused by faulting and
folding during the Precambrian orogenic events. Later,
from younger Precambrian through Jurassic time, there were several epeirogenic movements. These movements x'>- \
N\ \
after Solano Pirn. R lo T ?
Lineament High angle fault * Thrust fault Fig. 6. Structural map of Sonora, Mexico 21 produced minor folding and changes in the Sonoran deposi- tional basin of the Cordilleran geosyncline.
The younger Precambrian and Paleozoic sedimentary rocks are reported to have, both a northwest and a north east trend (King, 1939; Imlay, 1939; Fries, 1962; Wisser,
1966). The Mesozoic rocks have mainly a northwest trend with an occasional north trend. It appears that the
Laramide orogeny caused faulting and folding in a northwest direction, but some pre-Mesozoic sedimentary rocks, influ enced by the structural grain of older Precambrian rocks, deformed in a northeast direction.
In Tertiary time, strong north-northwest structures
developed during the Basin and Range orogeny. This orogeny
probably reactivated older faults. This diastrophic event
uplifted the Plateau section, probably by an epeirogenic movement. The Barranca section was strongly block faulted,
and the blocks were upraised on their western edge (King,
1939). The horsts and grabens, bordered by normal faults,
developed in the Basin and Range section; they show the
north-northwest structural trends very well. In the Basin
and Range section the present topography is strongly con
trolled by structure. Thrust faults were reported by King
(1939) in eastern Sonora. Fries (1962) believed that if
any thrust faults are present, they were formed before
Eocene time. The last movement known is a fault associ
ated with an earthquake around Arizpe in 1887. De Cserna 22
(1960) refers to the tectonic activity from mid-Cretaceous to Pleistocene time as part of the Mexican geotectonic cycle. GEOLOGY OF THE OPODEPE MINING AREA
Geomorphology
The thesis area lies in the western edge of the
Basin and Range section of the Sierra Madre Occidental
province. A regional north-south steep normal fault cuts
the study area at its eastern end and at least partially
controls the San Miguel River course. The rocks on the
west side of the fault have been raised with respect to
• the rocks on the eastern side of the fault.
The San Miguel River meanders slightly in its well-
defined wide channel. This is because of flooding during
the rainy season; the river is dry most of the year.
East of the river, there are 10- to 15-km-long
Baucarit(?) pediments. These pediments are not very high
and have narrow to broad, rounded tops; also they have a
semiparallel featherlike internal drainage. There is less
than 20 percent outcrop in this area, and the only rocks
present are a quartz monzonite porphyry and the Sonoran
granite. Outside of the area of study, about 10 km east
of Opodepe, rhyolite and basalt flows begin to crop out.
West of the river, the topography is more abrupt.
It rises fairly fast in some places, particularly west of
Opodepe where there is a 500-m change in elevation within
23 24 a short horizontal distance. Many of the highest moun tains are capped by northwesterly trending, vertically dipping, bedded, reddish quartzites, which are very resis tant to erosion. Sometimes this rock forms cliffs 20 to
30 m high mainly because of the vertical bedding and faulting. The top of these hills is fairly flat except for the semiparallel internal drainage controlled by the bedding planes.
Another fairly weather-resistant rock is a reddish- purple rhyolite porphyry, which crops out with a northwest trend. The hills are high with rounded peaks and steep slopes. The stream channels are very narrow and in some places there are 10-m waterfalls. The reddish-white
Creston granite is the last rock to mention that is fairly resistant to weathering. This intrusive rock forms high hills with narrow crests and steep slopes. This rock type has a particular east-northeast structural and textural trend; the trend is more apparent in the altered and mineralized area. The Creston granite crops out over a large area with an internal semidendritic drainage.
Some of the cuestas or slopes consists of Pre- cambrian andesite-diorite and gneisses. These rocks, known as the basement, are not very resistant to erosion; a phyllite or meta-andesite in the andesite-diorite group is especially weak. This phyllite along with the gneisses 25 also has an east-northeast structural and textural trend, similar to the Creston granite. The local drainage pattern is semidendritic and the few hills formed in phyllites and gneisses are low and rounded. These rocks are sometimes strongly fractured.
The dikes that crop out generally trend in an east- northeast direction and are moderately fractured. They are more resistant to erosion than the basement and form small hills, probably because the dikes are not more than 20 m wide.
A pinkish-white monzonite porphyry crops out next to the San Miguel River. This rock forms long pediments.
These pediments have a steep dendritic drainage pattern, which is partially fracture controlled. North and west of of the study area, the Sonoran granite is exposed. This intrusive rock appears to be part of a large batholith, and it is present over a large area. It has a well-developed dendritic drainage and forms a generally flat land. This granite weathers into typical rounded blocks, and the few hills present are small with rounded peaks.
Stratigraphy
The rocks present in the area range from Precam- brian to Quarternary in age, with much of the geologic sec tion missing (Figs. 3, 7, 8, and 9, in pocket). The rocks assigned to the Precambrian are andesitic to dioritic and 26 and are accompanied by major gneissic granites. This meta- morphic group is overlain by a series of steeply dipping quartzite beds of Paleozoic age. Later, during the Lara- mide orogeny, several plutons of granitic to monzonitic composition were emplaced, along with a rhyolite porphyry intrusive rock. Also some zones of brecciation developed during this period of tectonic activity. At the end of the Laramide orogeny or perhaps during the Basin and Range orogeny, dioritic and rhyolitic dikes intruded the older rocks. The last and youngest unit mapped is a series of poorly consolidated, horizontal beds of sands and gravels.
These beds can be correlated with the Baucarit formation.
To the author's knowledge, no previous detailed geologic work has been done in or around the Opodepe mining area, so no references were available to help date the dif ferent units encountered in the area. During the field work a tentative age was given to the different rock types.
The age assignment was based on field observations and on two intrusive rock samples dated later for Minera Opodepe
(Lodder and others, 1975).
Sedimentary Rocks
The oldest sedimentary unit mapped was a series of quartzite, sandstone, and shales beds. This unit crops out over a very large area, with consistently vertical bedding or dipping very steeply to the southwest or 27 northeast. The thickness of this sequence of beds is esti mated to be 200-300 m, but the actual thickness is not known. The basal member is a series of interlayered beds of medium-grained quartzites and quartz pebble conglomer
ates. This member is made up of five to seven layers, with each bed being from 2 to 3 m thick. The pebbles and
occasional cobbles are fairly well rounded.
The quartzitic member is generally reddish purple
to reddish pink; it consists of 90-95% quartz and 5-10%
orthoclase, with minor amounts of magnetite and hematite.
Most beds are strongly cemented by quartz, but there are
some that have a more friable texture. Some layers also
show brecciation, which appears to be of sedimentary
origin. The layers of shale and siltstone interbedded
with the quartz beds are generally 50 to 100 cm thick.
During the field work, particular emphasis was
placed on finding the contact between the quartzites and
the other rocks. This was not very fruitful, but based
on the field observations a tentative age was assigned
to this unit. The faulting and folding in the area made
it more difficult to find the key exposure.
The other sedimentary unit mapped is a series of
poorly consolidated, horizontal beds of sands and gravels.
This sequence of sands and gravels can be correlated to
the Baucarit formation of late Pliocene or early 28
Pleistocene age. This unit covers a large area east of the San Miguel River.
Igneous Rocks
Several intrusive rocks were mapped during the field work; the apparently oldest one is a grayish-white holocrystalline granitic batholith named the Sonoran granite. It has an average composition of 20% quartz,
25-30% oligoclase, 35-40% orthoclase with microcline,
10-15% biotite, 5% hornblende, and minor amounts of mag netite and sphene. This rock has characteristic fine grained, biotite-plagioclase-rich xenoliths and has aplite dikes. These dikes are less than 75 cm thick, and
they could have developed from a residual solution in the
same magma that produced the Sonoran granite. Biotite has
almost completely replaced hornblende, and there is weak
chloritization of biotite especially close to the contact with other intrusive rocks. The feldspars show weak
kaolinization, probably caused by supergene effects.
There are a few quartz veins in this intrusive rock; they
contain occasional small amounts of pyrite and molybde
nite.
Because of its textural, weathering, and field
characteristics, the Sonoran granite was considered to be
of pre-Laramide age. But an age date done on this intru
sive by Miners Opodepe gave a date of 57 ± 2 m.y., which 29 tells us that it was emplaced in early Eocene time. This batholith crops out over a very large area.
Monzonite. West of the town of Opodepe a reddish- gray biporphyritic monzonite is exposed. The composition of this intrusive rock is 5-10% quartz, 40% orthoclase and microcline, 30-35% plagioclase (oligoclase and albite),
10-15% biotite, and 5% hornblende, with minor amounts of magnetite and sphene. The phenocrysts, which make only
10 percent of the rock, are biotite crystals 4 mm long and feldspar crystals 6 mm long. The rest of the crystals are less than 3 mm long, and the contrast in size is notice able in hand specimens. This stock appears to be of a very limited size and its areal extent is less than one square kilometer.
This monzonite is older than the quartz monzonite porphyry and younger than the Creston granite; it was not possible to determine the relative age of this stock with respect to the Sonoran granite. The only megascopic dif ference is that the monzonite looks fresher than the batholith. Biotite has partially replaced hornblende, and the feldspars are partially changed to clay due to supergene effects. No sulfides and no quartz veining were noted.
Quartz Monzonite Porphyry. The youngest plutonic intrusive rock mapped is a pinkish-white quartz monzonite 30 porphyry. The average composition of the groundmass is
20-25% quartz, 35-45% oligoclase, 25% orthoclase, and 10% biotite, with minor amounts of magnetite. The matrix is fairly equigranular, with subhedral to euhedral crystals.
The orthoclase phenocrysts make from 15 to 40 percent of the rock.
This rock is generally fresh. But close to the contact with the Creston granite it has moderate propylitic and weak argillic alteration. The sulfides present, although in small amounts, are pyrite, molybdenite, and chalcopyrite. Molybdenite and chalcopyrite are generally found with quartz veins. Pyrite is more abundant; it occurs associated with quartz and in fractures. This intrusive rock might be responsible for the mineraliza tion.
The quartz monzonite porphyry crops out in the eastern part of the area close to Opodepe and in the western part of the area at Rancho la Tinaja. Although this intrusive rock does not crop out in the middle part of this area, it is probably under the older rocks, inas much as the stock appears to have been emplaced along the major old east-northeast structural trend. A fresh sample of this porphyry was dated and found to be 55 ± 2 m.y. old; this indicates that the stock was emplaced dur ing the later part of the Laramide orogeny. 31
At Cerro Creston, there is a small outcrop of a pinkish-white quartz orthoclase porphyry close to the top of the mountain. This rock has up to 40% phenocrysts in a glassy groundmass. In some places there are plagio- clase phenocrysts instead of orthoclase phenocrysts.
Because of the characteristics of this porphyry, it is reasonable to assume that this rock is a dike or apophysis of the quartz monzonite porphyry.
Rhyolite Porphyry. A reddish-purple rhyolite porphyry crops out on the northwestern portion of the study area. The composition of this porphyry is 25% quartz, 20% orthoclase, 5% albite, 50% of a glassy matrix, and minor amounts of magnetite. This rock has a charac teristic and well-developed graphic texture. This intru sive rock is mainly fresh, with weak sericitization of the feldspars, probably due to supergene effects. A very few quartz veins were noticed, but no sulfides were iden tified.
No conclusive evidence was found to give this rock a relative age. Except for a few places where this stock is in contact with the Sonoran granite, the rhyolite porphyry appears to be younger. This intrusive rock crops out over a very large area with a general northwesterly topographic trend. J?he northwestern lineaments are characteristic of the structural trends formed during the 32
Laramide orogeny, and this stock appears to have intruded older units at a late stage in this tectonic event.
Dikes. The last igneous event is marked by the intrusion of a series of dioritic and rhyolitic dikes.
The dioritic dikes are greenish gray, equigranular, and have 40% oligoclase, 25% biotite, 5% hornblende, 10% orthoclase, and 20% glassy matrix. The biotite is weakly chloritized. The rhyolite dikes are whitish pink, with plagioclase, orthoclase, and quartz phenocrysts in a glassy groundmass. The phenocrysts locally make up to 30 percent of the rock. The dikes are generally fresh and have occasional quartz-pyrite veinlets. They are gener ally long and narrow.
Breccia. Several breccias were mapped by the geologists of Cia. Minera Opodepe, and the breccias reflect directly the amount of tectonic activity that the area has gone through. The breccia at Cerro Creston appears to be a breccia pipe and consists of angular rotated fragments of different rock types. These frag ments are strongly sericitized and are cemented with quartz. Small amounts of pyrite, molybdenite, and chalcopyrite are associated with the quartz veining.
Metamorphic Rocks
All the rocks assigned to the Precambrian have some degree of metamorphic texture with a general 33 east-northeast textural trend. The field relationship of these rocks to other units makes them the oldest ones in the area.
Augen and Banded Gneisses. The oldest metamorphic units consist of two gneisses, a whitish-gray augen gneiss and a gray banded gneiss. They are similar in composition except that the augen gneiss has up to 20% orthoclase phenocrysts, and the crystals can be from 1 to 3 cm long. The groundmass consists of 20-30% ortho clase, 20-25% biotite, 30-40% plagioclase, 15-20% quartz, and 5% hornblende, with minor amounts of magnetite and spinel. The texture is very noticeable because of the black (biotite) and white (feldspar) banding.
Biotite has partially replaced the hornblende, and the gneisses show weak chloritic alteration at the contact with younger intrusive units. Close to Cerro
Creston hydrothermal fluids have caused strong chloriti- zation of biotite and moderate kaolinization of feldspar.
This unit does not seem to be very receptive to mineral— ization, but there is some quartz veining with pyrite and occasionally with molybdenite.
Andesite to Diorite Group. The next oldest unit is a group of rocks of andesitic to dioritic composition with various degrees of metamorphism. The age relationship between this unit and the gneisses is not very clear, but 34 there are some indications that the gneisses are older.
The andesites are brownish green with small amounts of plagioclase and biotite as phenocrysts. Sometimes the rock has been so strongly metamorphosed that it resembles a phyllite. The diorite is a dark-green equigranular rock, consisting of 50% andesine, 10% orthoclase, 5% quartz, 2-30% biotite, and 10% hornblende, with minor amounts of ilmenite and garnet.
The mafics are weakly chloritized, and in some parts close to Cerro Creston the feldspars are moderately argillized and weakly sericitized. These rocks crop out throughout the area, and they do not appear to have been receptive to mineralization. In some places there is moderate quartz veining, but sulfides are not abundant.
Creston Granite. The youngest unit with a meta mo r phi c texture is a pinkish-gray, slightly foliated
granite, called the Creston granite. The composition of
the Creston granite is 25-35% quartz, 30-40% orthoclase with microcline, 20-30% plagioclase (oligoclase and
albite), and 5-10% biotite, with minor amounts of mag
netite, zircon, and ilmenite. At Cerro Creston the
amounts of quartz and orthoclase both increase, making
the foliation more conspicuous, particularly in the
argillic and quartz sericitic alteration haloes. This
unit crops out over approximately 12 percent of the area. 35 and it is the rock most strongly altered and mineralized by hydrothermal fluids.
Geologists from Cia. Minera Opodepe were able to distinguish certain alteration zoning in the area. The area of alteration has an oval shape with a potassic cen ter, a phyllic halo, and an outer propylitic halo (Lodder and others, 1975). There are also areas with strong silicification and argillic alteration. The alteration haloes' do not appear to be concentric. The available information on this hydrothermal system shows a general similarity with the Lowell and Gilbert (1970) model for porphyry ore deposits.
This unit is the host rock for the pyrite, molyb denite, and chalcopyrite mineralization, with these minerals being most abundant in the quartz sericitic halo of the alteration zone. Pyrite is found mostly associated with quartz veining, but it also occurs in fractures and in lesser amounts as disseminated grains. Molybdenite and chalcopyrite are less abundant than pyrite; they occur mostly in small quartz sericitic veinlets. Chalcopyrite is even less common than molybdenite. Much of the'sul fides at the surface have been oxidized and leached leav ing a limonitic staining. 36
Structural Geology
As mentioned before, the area of study lies in the western edge of the Basin and Range geomorphic section.
Several of the structural characteristics of the late mid-
Tertiary orogeny were recognized. Because of the large number of older units exposed, structural features reflect most of the important tectonic events that have affected the area.
The geologic map (Fig. 3, in pocket) shows the actual structures mapped during the field work and some later structural data that were projected or added as part of the geologic interpretation. Also several prom inent lineaments are indicated as possible structural features. There are two topographic trends in this area.
One has an east-northeast direction, is present in the older rocks, and is well distinguished in the geologic map. The other trend has a northwest direction; it is outlined by the rhyolite intrusion and the quartzite sequence.
Folding
The only unit where structural deformation was noticed is in the quartzite sequence. This series of beds has a characteristically N. 40o-60° W. strike and
steep dip; in some places the beds are vertical. This unit crops out throughout the area as small blocks, but 36
Structural Geology
As mentioned before, the area of study lies in the western edge of the Basin and Range geomorphic section.
Several of the structural characteristics of the late mid-
Tertiary orogeny were recognized. Because of the large number of older units exposed, structural features reflect most of the important tectonic events that have affected the area.
The geologic map (Fig. 3, in pocket) shows the actual structures mapped during the field work and some later structural data that were projected or added as part of the geologic interpretation. Also several prom inent lineaments are indicated as possible structural features. There are two topographic trends in this area.
One has an east-northeast direction, is present in the older rocks, and is well distinguished in the geologic map. The other trend has a northwest direction; it is outlined by the rhyolite intrusion and the quartzite sequence.
Folding
The only unit where structural deformation was noticed is in the quartzite sequence. This series of beds has a characteristically N. 40o-60° W. strike and
steep dip; in some places the beds are vertical. This
unit crops out throughout the area as small blocks, but 37 toward the south-central part of the area there is a long continuous outcrop of quartzites. There are more long con
tinuous quartzite outcrops outside of the area of study, southwest of Rancho la Tinaja. The blocks or remnants of quartzites show a change in dip in several places. Because of all the fracturing and faulting, the bedding is obscured and in some places it was very difficult to obtain a true
attitude for these beds.
The quartzites on top of Cerro del Resbaladero have
a general northwest strike. On the south side of the moun
tain the beds dip very steeply southwest, but on the north
side they dip northeast. There are two normal faults that
have downfaulted the sedimentary sequence to the north.
These rocks are strongly fractured, and in some places it was very difficult to measure the actual strike and dip of
the bedding. The quartzites in the central portion of the
mapped area also have a change in dip. At the top of the
mountain the beds dip 40° SW. and the dip becomes steeper
toward the southwest side of the hill. The general strike
is N. 60* W. Another quartzite remnant at Cerro Colorado
shows a change in dip; on the top of the east side of this
outcrop, the beds dip very steeply and then flatten toward
the base and toward the west side of this hill. Generally
the beds dip southwest with a N. 40° W. strike.
The only other place inside the mapped area where
the quartzite shows a change in dip is just north of 38
Rancho la Cienega. On the west side of the hill the beds dip very steeply, but at the top the beds dip 45° SW. and strike N. 50° W. Here the rocks are strongly fractured.
Outside of the area of study several outcrops of quartzites were found. At Cerro el Batamote the sedimentary rocks show a distinctive change in dip from gentle at the top to steeper on the south side of the hill. The beds here are less disturbed and less fractured than in the other quartzite remnants.
From the available information, it can be safely concluded that the area was subjected to southwest- northeast compressional forces during the iaramide orogeny.
These forces produced very tight folding in the sedimentary sequence and left these beds with a generally northwest attitude. When the quartzite beds were being folded, ten sion joints developed parallel to the fold axis. The effects of these compressional forces, which produced a lot of tension fractures and faulting, make it very diffi cult to find the depositional contact of this sedimentary sequence. Probably the change in dip mapped in several of the quartzite remnants associated with the steeply dipping beds is the best evidence in supporting the pro posed theory of very tight folding of the sedimentary sequence. 39 Fractures
Although the rocks throughout the area are strongly fractured, some units are more intensely broken than others. The degree of fracturing was influenced by the closeness to a structure or an intrusive contact and by rock type. The best evidence that rock type influenced the intensity of fracturing is in the strongly metamor phosed andesite, phyllite. This rock shows a very closely spaced pattern of fractures with different strikes. This rock is so broken up that it crumbled upon attempts to get a hand specimen.
From the available readings, the prevailing joint directions are N. 35°-45c E., N. 60o-70° E., N. 30° W . , and N. 40o-60° W. In the field, the prevailing joint directions were recorded but a different symbol was used wherever the fractures were closely spaced and with
several directions. This can be seen in Fig. 3, especially
close to the regional fault on the east side of the mapped
area. This distinction was necessary because the second
symbol for joints indicates closeness to a structural
feature, probably a fault.
The quartzites, being a competent unit in this
area, have generally developed orthogonal sets of joints.
One set is parallel to the bedding and the other is
perpendicular. The set perpendicular to the bedding 40 developed as tension fractures, and the other set is prob ably the result of bedding-plane slippage.
Faults
From the geologic map it can be discerned that there are three general directions of faulting: northwest, north, and east-northeast. Probably the oldest structure is the fault contact between the Creston granite and the andesite group. This structure is restricted to the older units, has a N. 70* E. strike, and is offset by two left- lateral faults. During the Laramide orogeny, the area was subjected to vertical and lateral forces and two sets of faults developed. One set consists of high-angle normal faults, usually characteristic of the guartzitic sequence, that formed parallel to the bedding. The other set is perpendicular to the bedding with a general northeast direction. This second set appears to have vertical and lateral movements, but the two components are not always present. The faults parallel to the bedding occurred earlier than the ones perpendicular to the bedding.
There is one structure in the north-central por
tion of the area that has very peculiar characteristics.
This structure, which has a brecciated character, is probably an old fault, and it has concentrated large
amounts of a mixture of CaCO^ and SiOg at each end of
the trace of this structure. It appears that parts of 41 these old zones of weakness were occupied by fumaroles or conduits where solutions rich in CaCO^ and SiOg passed through and that some of these solutions solidified, form ing two distinctive little hills. This fumarolic activity might be related to the Late Cretaceous volcanism. Vol canic rocks crop out east of the San Miguel River, where rhyolitic and basaltic flows have been recognized.
The youngest set of faults has a general north- northwest direction and is related to the Basin and Range orogeny. The San Miguel River is partially defined by one of the regional faults that produced the horsts and grabens characteristic of this geomorphic section. This structure is very well expressed just south of La Canada del Corral.
At this point the quartz monzonite porphyry comes in con tact with the Baucarit formation, and the contact is a
fault. Here there is a small topographic expression of the regional fault, which appears as a linear feature, but even though the sediments are higher, a fault scarp has not developed. Close to the contact with the sediments,
the quartz monzonite porphyry is strongly fractured, and
several of the fracture planes have slickensides. This
structure appears to be in some places more of a fault
zone, and it is partially defined by the wide zone of
strongly fractured rock. There is another fault east of
Cerro Creston that has the same general orientation. It 42 shows a right-lateral movement and offsets the older units and a dike.
In some drill holes, a very low angle structure was encountered under Cerro Creston; it appears to be a low-angle normal fault dipping north. This structure also marks the contact of the Creston granite with the quartz monzonite porphyry. There is not enough surface evidence to fully explain this feature; all of the infor mation pertaining to this structure has come from drill holes.
During the geologic interpretation, several faults were continued or added to better explain the structural history of the area. Several prominent lineaments were
also included in the geologic map. These lineaments
probably reflect some structural features, but there were
no surface expressions of them. A more detailed descrip
tion of these lineaments will be given in the section on
photogeology.
Foliation
Even though all the rocks with metamorphic texture
were assigned to the Precambrian, the only ones with a dis
tinctive and measurable foliation were the gneisses.
Throughout the area, this unit shows a general, very
steep, N . 40o-80° E. foliation or textural trend. Although
there are very few readings, the foliation appears to 43 outline an elongate denial structure, probably caused by the emplacement of the quartz monzonite porphyry.
Dikes
Dikes are more abundant south of Cerro Colorado.
This may be because they have a relationship to the quartz monzonite porphyry and it may be only apparent due to the greater amount of detailed work done in that area by Cia.
Minera Opodepe. The dikes have predominant east-northeast and north orientations. Their emplacement was probably affected by old structural features.
The dikes are mostly rhyolitic but some are dio--
ritic. The dikes appear to be contemporaneous, but because
of the normal sequence in magmatic differentiation the
dioritic dikes may be slightly older.
Breccias
Several breccias were recognized and mapped by the
Minera Opodepe staff. Most of these breccias show a true
intrusive character, but a big area to the southern part
of the mapped area that was outlined as a breccia is less
distinct. Although the area has in some parts a brecciated
character, it consists mostly of faulted blocks of various
rock types. Some of the blocks are 100 m long (Lodder and
others, 1975). 44 Mineralization
Because of the several tectonic events that have affected the area, the rocks are strongly fractured. This has caused an excellent ground preparation for any min eralizing event at Cerro Creston. The mineralization here is mostly in fractures and associated with quartz veins.
The mineralized fractures do not have a preferred orienta tion, and the mineral deposit can be classified as a stock work. EXPLORATION TECHNIQUES USED IN THE OPODEPE MINING AREA
The encouraging results of the preliminary evalua
tion of Cerro Creston by Minera Opodepe geologists led to a regional evaluation throughout this area. Two techniques were used: one was a geochemical survey program and the other a photogeologic interpretation of the area.
Photogeology
As mentioned before, the mapping was done on aer
ial photographs. Along with the mapping, a photogeologic
interpretation of the area was done; it proved to be very
useful and it helped speed up the field work. In this sec
tion, a brief photogeologic description of each unit will
be given, and at the end, a summary will point out the
distinctive characteristics of the area. Black-and-white
and color photographs were made available by Cia. Minera
Opodepe at 1:10,000 scale. Black-and-white photographs
were obtained from the Consejo de Recursos Minerales at
1:50,000 scale.
The amount of vegetation and sunlight have a direct
effect on the tone and color shown by each rock type. For
these reasons, some rocks show different colors and tones
within their areas of outcrop.
45 46
Photogeologic Description of the Units
Gneisses. This unit crops out in several parts of the area. Generally, the gneisses are not very resistant to weathering, and they form hills of low to moderate relief with rounded crests and gentle slopes. Occasionally where this unit is capped by a more resistant unit it will form very steep slopes. These rocks show a bright-green color with faint shades of white, probably due to the band ing. On the 1:10,000-scale, black-and-white photographs, the gneisses have a medium-gray tone. At the 1:50,000- scale, they show a very smooth, medium-gray tone.
A semiparallel and coarse dendritic drainage pattern was noticed in this unit, and the density of streams pro duces mostly the medium texture of the gneisses. The semi parallel pattern develops where these rocks crop out on the hillside and where they are capped by a more resistant unit. The dendritic pattern with some pincerlike ends develops where this unit crops out over a wide area and within the valleys. Usually only brush and small trees grow in these rocks, but some large trees were noticed.
Because large trees are more abundant in the southwest corner of the mapped area, they give a dotted texture to this unit.
Andesite-Diorite Group. These rocks were mapped in different parts of the study area. This unit, particularly 47 the "phyllites," is similar to the gneisses in that it is not resistant to weathering. This group forms low rounded hills with gentle slopes, and where it is capped by a more resistant unit, very steep slopes have developed.
In the color photographs, these rocks show a dark- green to brown color, and if bleached they have a light- green color. In the black-and-white photographs, this unit has a medium-gray tone, but darker than the tone shown by the gneisses. Even though a characteristic drainage pat tern was not recognized, two different patterns were noticed. The first is a semiparallel pattern; it is better developed where the rocks form steep slopes. Where this group of rocks crop out in valleys or flat terrain, it develops a dendritic-type drainage. This unit has the same general texture as that of the gneisses, except it may have a slightly finer texture, especially on the lower lands.
Being in a semidesert region, the area is not heav ily vegetated; vegetation is represented by brush and by palo bianco, palo verde, mesquite, and sahuaros growing among the rocks. The area where this unit crops out is no exception, and mostly brush with some trees grow on it.
Creston Granite. The Creston granite is the second most abundant rock type in the area. It is fairly resis
tant to weathering and forms hills of high to medium
relief. The highest peaks are present in Creston ridge. 48 where they have very narrow crests with steep slopes. The reason is probably due to the strong quartz veining and some quartz flooding in the argillic and phyllic alteration haloes. In the rest of the area the hills are smaller, rounder, and have more gentle slopes. In most of the area, exposures of this unit are topographically higher than those of other units except for quartzites.
On color photographs this rock shows a light-to-tan
color with patches of red in the alteration zone. This
light color is very noticeable in the alteration zone. In
the black-and-white photographs the rock shows a light-gray
tone that is usually lighter than the tone of the gneisses.
This unit has developed a dendritic drainage pattern with pincerlike ends in the area southwest of Opodepe and
in the southwestern corner of the mapped area. In other
areas where this unit crops out, a coarse dendritic to sub
parallel drainage pattern developed. This pattern is very
characteristic of the area with high topographic relief.
The vegetation in this unit is similar to that of
other units, except for the northern slopes of Creston
ridge. Here there is a heavy concentration of walnut and
live oak trees, probably due to the elevation, less sun
light, and the altered rock. The heavy concentration of
trees on this ridge is unusual in this area and only occurs
here and on the next ridge south of Creston ridge. 49
Quartzites. The quartzites are found mostly as blocks or remnants on top of older rocks. There is only one place, in the south-central part of the mapped area, where the sequence forms a narrow long continuous outcrop.
These beds form the highest peaks in the area due to their strong resistance to erosion and weathering. Because of their vertical attitude, the beds are very distinctive in the photographs. They have a tendency to form cliffs. Usu ally the blocks are long and narrow, and they have the same general orientation as the beds. Due to the strongly frac tured character of the quartzites, large quantities of debris accumulate on top of the outcrops; this sometimes obscures the bedding, making it difficult to be recognized and mapped.
This unit shows a pinkish-white color and a light- gray tone. There are areas that have a darker tone and more reddish color probably because of higher concentra tions of hematite. The talus also shows a reddish color.
The quartzitic remnants have a parallel drainage pattern characteristic of sedimentary rocks; the drainage pattern is not well developed, probably because of the fractured character of this unit. Where there are large amounts of debris accumulated on the sequence, a coarse dendritic pattern starts to develop. The streams are controlled by the bedding and joints. 50
Hot much vegetation grows on these rocks; mostly
grass is found on top of the hills with occasional live oak
trees. There is one type of tree that seems to grow mostly
in these rocks or close to them, especially where there is water. These trees are called by the local people uvalamas.
The lower contact of the quartzites appears to be impervi
ous, evidenced by the fact that several springs have been
found close to where the contact should be. Probably
because the quartzites are strongly fractured, they make
good water reservoirs.
Sonoran Granite. Sonoran granite crops out over a
very large area, forming a fairly flat terrain and low
rounded hills. Where the aplite dikes are wide enough,
they are noticeable in the photographs. The aplite dikes
are restricted to this unit. The area of Sonoran granite
in the southwest corner of the mapped area shows moderate
topographic relief; here the rock is slightly altered and
has some quartz veins. The veins have a general east-
west orientation.
The batholith shows a white to light tan color and
a light gray tone; this is very noticeable where there is
little or no vegetation. The area has a fairly uniform
color, except for the area that is more heavily vegetated,
which has a darker tone. Because the granite weathers
very easily and uniformly, a dendritic drainage pattern has 51 developed in it. At the base of the mountains and in the north part of the mapped area a semiparallel drainage pat tern was recognized. This pattern is associated with this rock where it comes in contact with other rocks.
Mesquite trees and brush grow on this rock. Large
trees occur mostly along streams but some are scattered on
top of the hills. Brush grows mostly on the hillsides.
The light color of this rock, the scattered trees, and the
well-developed internal drainage give the area a fine
dotted texture. In the southwest corner of the mapped
area, a coarser texture was recognized. The appearance of
the batholithic rock is distinctively different from that
of the other rocks.
Monzonite. This intrusive rock crops out over a
relatively small area, just west of the town of Opodepe,
and very little can be said about it. The area where
this rock crops out is fairly flat, and it is cut by only
a few streams.
In black-and-white photographs, this unit shows a
light- to medium-gray tone, slightly darker than the tone
shown by the Creston granite and similar to the gray tone
of the gneisses. The few streams that cut this area have
a semiparallel drainage pattern. Brush-type vegetation is
very abundant, and some mesquite trees were identified. 52
Quartz Monzonite Porphyry, The quartz monzonite porphyry crops out over a smaller area than the Sonoran granite and mostly in the eastern part of the mapped area.
It forms a fairly homogeneous flat pediment, strongly dis sected by streams, and low narrow elongate ridges or hills.
This intrusive rock shows a white to light-tan color and a light-gray tone. The tone is very similar to the tone of the Sonoran granite but duller. Close to Cerro
Creston the color becomes very similar to that of the
Creston granite. In some places a red color was noticed due to stronger oxidation.
The rock has a fairly well developed subdendritic drainage pattern with some pincerlike ends, and it has peculiar arborescent short streams. Close to the regional structure that defines the San Miguel River, the streams show a partial fracture control. The exposed pluton is not heavily vegetated, but brush grows fairly well on it.
There are mesquite trees growing along the stream and some
scattered along the top of the ridges.
The drainage pattern gives the area a fine texture,
and the scattered trees a dotted character. The texture
is very similar to that recognized in the Sonoran granite.
The texture becomes coarser close to the contact with the
Creston granite; this is especially apparent at Cerro
Creston. 53
Quartz-Orthoclase Porphyry. This rock is in contact with the altered Creston granite and crops out over a very
small area on the southeast slope of Cerro Creston. The
rock has a light-brown color and a bright, light-gray tone,
very similar to the color and tone of the Creston granite;
this is expected because the two rocks have similar compo
sitions. There appears to be a slight change in the type
of vegetation from that which grows on the Creston granite.
In this porphyry, light-colored trees are more abundant;
they are palo bianco, palo verde, and torote. Because of
its composition and characteristics, this rock was previ
ously considered a subunit, a dike or apophysis of the
quartz monzonite porphyry.
Rhyolite Porphyry. This intrusion does not crop out
in the zone of alteration and mineralization. The area
where the rhyolite porphyry is present has a general north
west topographic direction. The topography is fairly
rugged, and this rock forms high hills with smooth rounded
ridges and steep slopes. Exposures toward the northwest
corner of the mapped area have less topographic relief.
No color photographs were available for the area
where this intrusive rock crops out. In the black-and-
white photographs, the rock shows a medium-gray tone, simi
lar to the one shown by the andesite group. The southern
slopes of this area have a lighter tone than the northern 54 slopes; probably because the southern slopes receive more sunlight and the northern slopes are more heavily vegetated.
Throughout the area, a coarse dendritic drainage pattern was recognized on exposures of rhyolite porphyry.
Near the northwest corner of the mapped area there is a small area that has a better developed dendritic drainage pattern with some pincerlike ends. This probably developed because of the lesser topographic relief and more debris accumulation in the lower parts.
This unit is not heavily vegetated, and it is mostly covered by grass with small amounts of brush. In some of
the northern slopes of the highest peaks, live oak trees grow. Also some mesquite trees were recognized in the
lower parts and along the streams.
Dikes. Two types of dikes are present in the area
of study; the most common ones have a rhyolitic composi
tion, and the other dikes have a dioritic composition. The
rhyolite dikes sometimes form long narrow ridges, but the
diorite dikes do not stand above the other units.
The rhyolite dikes show a whitish-yellow color and
a light-gray tone; the diorite dikes have a light-purple
color and a dark-gray tone. Because of their small dimen
sions, the dikes have not developed any internal drainage
patterns, but they affect the drainage in the adjacent 55 rocks. Mostly grass grows on these dikes, along with some small trees.
Breccias. Several areas were outlined as breccias, but most of them are very small, except for one area in the south-central part of the mapped area. The breccia on top of Cerro Creston is very resistant to weathering, and it forms cliffs on almost all sides. The other small breccias do not have any topographic characteristic. The large and less distinct brecciated area in the southern part of the mapped area forms a high narrow ridge with very steep slopes.
The Creston breccia shows a lighter color and tone than the Creston granite. The other small breccias show a very distinctive bright-red color and a dark-gray tone; their tone is slightly darker than the tone of the ande site. The bright-red color is due to the strong oxidation of the sulfides. The large brecciated area shows a light- brown color on the southern slope and a brown color on the northern slope. The reason is that the northern slope is more heavily vegetated and the southern slope receives more sunlight.
Inasmuch as most of the breccias are very small, the only one that has any internal drainage is the large brec ciated area in the south-central part of the study area.
Mainly it has a semiparallel drainage pattern. The northern 56
slope of the large brecciated area is heavily vegetated with large concentrations of live-oak trees. On the south
ern slopes, mostly brush and grass grow, but there are some
palo bianco and mesquite trees.
Iron Oxide-cemented Material. This material was
only identified over a very small area on Oreston ridge,
close to the Oreston breccia. The iron oxide-cemented
material shows a dark-brown color and a dark-gray tone
similar to the gray tone of the diorite dikes. The dark
color is due to the iron and manganese oxide cement. Only
a few trees appeared to grow on top of this material.
Alluvium. Most of the mapped alluvium occurs to
the east of the San Miguel River. There is also a small
area with alluvium west of the river, in the southeast cor
ner of the mapped area. The alluvium forms very long nar
row pediments of low relief. Aside from the generalized
expression, there appears to be at least two members in
this unit. One member is strongly dissected and forms
narrow ridges with steep slopes. The other member has a
more mesa-type geomorphic expression, with broad rounded
pediments and steep and sometimes vertical slopes.
One member shows a brown color and a medium-gray
tone, the other has a light-brown color and light-gray
tone. Where there is no vegetation, the second member has 57 a yellowish color. An internal drainage has developed better in the first member, which has a dendritic drainage pattern with featherlike short streams. The second member has a semiparallel drainage pattern, consisting of short streams.
The first member is heavily vegetated, mostly with brush and small trees. This vegetation is partially responsible for the dark tone of this member. The other member has less vegetation, mostly grass and some scattered trees. In some parts, this second member has almost no vegetation at all. Mesquite trees are common near the streams.
Usually the second and younger member is found on top of the first member, and the drainage pattern changes as it goes from one member to another.
Summary
Even though not all the rocks have identifying characteristics, the rocks can be considered together in several groups of distinctive characteristics. . The first group is made up of the Sonoran granite and the quartz monzonite porphyry. These rocks form a flat terrain, strongly dissected by streams, and present a white or light-gray dotted texture. There were no great photo graphic differences between these two intrusive rocks. 58
The second group includes only the sedimentary sequence. The quartzites show a white-pink color and have very little vegetative cover. These rocks are very resis tant to weathering and have a tendency to form cliffs. The bedding is very easily recognized, due to the vertical attitude of the beds.
Only the dikes are included in the third group. The diorite dikes do not stand above the other units, and even though they have a characteristic color, they can be only recognized where found intruding light-colored rocks.
Because the rhyolite dikes have some topographic relief, they are more easily recognized. These dikes show a light color, and very little vegetation grows on them.
The alluvium pediments make up the fourth group. To the east of the river, the sediments form long narrow pedi ments. They are strongly dissected by streams and have a characteristic featherlike drainage. On the west bank of the river, the sediments are less dissected and form more of mesa-type pediments.
All the rest of the units, which have the same general topographic expression, are considered in a fifth group. The area where these units crop out shows high topographic relief with a subparallel- to subdendritic- type drainage. In this respect, the color photographs become very useful, and further subdivisions could be made. In the first subgroup the Creston granite and the 59 quartz-orthoclase porphyry were put together. These rocks have a light-tan to light-brown color with a large concen tration of live-oak trees on the northern slope of the
Creston ridge. These rocks have the lightest color and tone of all the rocks in this group.
The second subgroup is the broadest one because it
includes the gneisses, the andesites, the rhyolite porphyry, and the monzonite. In the color photographs the gneisses
show a bright-green color, while the andesites have a
greenish-brown color. In the black-and-white photographs, the gneisses and the monzonite have a medium-gray tone,
slightly lighter than the tone shown by the andesites and
the rhyolite porphyry. In some places, especially in the
valleys, the andesite develops a fine texture. The outcrop
area of the rhyolite porphyry has a characteristic north west topographic trend.
The third and last subgroup is made up of all the
breccias. The only characteristic of the Creston breccia
is its resistance to weathering it; it is bordered by
cliffs on almost all sides. The large and less distinctly
brecciated area in the south-central part of the mapped
area does not have any particular characteristic. The
other small breccias show a bright-red color, which makes
them easy to differentiate from the other rocks.
The photographs at a 1:10,000 scale proved to be
very useful during the field work and in identifying each 60 unit. On the other hand, the photographs at a 1:50,000 scale give an excellent synoptic view of the whole area.
Lineament Analysis
At the beginning of the field work, all the linear features in the photographs were outlined (Fig. 10, in pocket). Several of these lineaments had a surface expres sion that defined their character; an example is the fault east of the San Miguel River. Some other lineaments with a strong photographic character such as the one west of
Opodepe had no field expression. The lineaments with a strong photographic expression were included on the geo
logic map because they probably reflect some concealed
structural feature, maybe a fault or a strong joint direc tion.
Later a lineament analysis was done to see if the
lineaments are related to the structural framework of the
area. A histogram (Fig. 11) was made from the orientations
of all the lineaments, and it was found that the predomi
nant orientations are: N. 30o-35° E., N. 70° E., N. 85°-
90° E., N. 0e-10° W . , N. 45°-550 W., and N. 70° W. Even
though in detailed field work most of these lineaments will
not turn out to be faults, they generally reflect the
stress directions of the forces acting during the different
tectonic events. The lineaments with N. 70° E. and N. 85°-
90° E. orientations are probably related to the older NUMBER Lineament histogram Lineament IETO FO NRHC) NORTH C FROM DIRECTION H o> 62 orogenies, while the ones with N. 25°-30° E. and N. 45°-
55° W. orientations reflect the direction of structural deformation produced during the Laramide orogeny. The
N. 0°-10o W. lineaments are related to the direction of regional deformation caused by the Basin and Range orogeny.
Again, the predominant regional structural trends are
N. 0°-10o W., northwest, and north-northeast. The local structural trends are similar to the regional ones; they are northwest, north, and east-northeast.
Geochemical Trend Analysis
A stream sediment survey was done in the first phase of the regional evaluation. The purpose of this survey was to evaluate and possibly to understand the distribution of molybdenum and copper over a large area close to Opodepe
(Fig. 12, in pocket). Later, as part of the geochemical program, a detail rock chip survey was carried out on
Creston ridge. This survey consisted of 14 lines of dif ferent lengths; 10 lines were 200 m apart and 4 lines were
400 m apart; samples were collected every 40 m (Fig. 12).
The samples from all the surveys were analyzed by Cia.
Minera Opodepe for molybdenum and copper content.
Geostatistics
Trend surface analysis is the geostatistical method used in this study to analyze the geochemical data obtained in the Opodepe mining area. The purpose of the trend 63 surface analysis is to separate the map data into two com ponents : the regional trend and the local fluctuations.
Davis (1973, p. 324) defines a trend surface as "a linear function of the geographic coordinates of a set of observa tions so constructed that the squared deviations from the trend are minimized." For this study, the Kansas State
Geological Survey computer program (O'Leary, Lippert, and
Spitz, 1966) was used to define any trends in the available data. The computer print-out gives a trend surface map, a plot of the residuals, and a plot of the original geochem ical values.
The computer program provides the user with a sum mary table of the several calculated statistical terms of the polynomial equations of orders 1 through 6; these terms were used to find the best model or fit for the geochemical values. A brief explanation of statistical terms will be provided to help the reader who is not familiar with this technique. These polynomial equations are calculated by using all the original samples for a metal (Z) to produce the equation where the metal value is a function of the X and Y coordinates, e.g., a second-degree equation.
Z=b+X+b0 +Y+ b-X2 + b.XY + bcY2 ' O 2 3 4 5 where Z is the computed value at a particular coordinate,
X is the easting coordinate, Y is the northing coordinate. 64 and the bs are the coefficients calculated by the trend program.
The calculated statistical terms given in the sum mary tables are: SS , SS , SS , R2 , R, and S. SS. is u 2T6Cj u the total sum of squares of the dependent variable, also referred to as the total variation, and it is calculated by the formula:
<^=0 z > SSt - *1=0 z2 Ei=o
n /N O SS E res i=o (Z-Z) and
- SS res
SSreg is the sum of squares explained by the trend.
After the three sum of squares have been obtained, 9 the goodness of fit (R ) can be calculated. This value explains the fraction of the total variation explained by the trend. 65 2 R SS t and
S = * To find the best equation that would fit the data, the F test for significance is used (Davis, 1973, p. 341- 342). The F test is a test of the null hypothesis and its alternative. The null hypothesis can be stated as: Ho :61=62=63= ••• 6n = 0 62/63/ ... ^ 0 The hypothesis to be tested is that the partial regression coefficients are equal to zero, which means that if they are, there is no trend, hence no useful polynomial equa tion. The test is done by comparing the computed value of F (F^) with the table value of F (F^.) . If F^ is greater than Ft , the null hypothesis HQ is rejected, and the alter native is accepted. If is accepted, the equation is statistically significant. The Fc value was calculated and compared with the F^_ value for each equation in order to find the best model (highest order equation) for the geochemical data. F^ was found by computing: 66 Travel times were calculated using an average value for K of 951 m/day as reported by Turner (1962) for Planet Valley alluvium and two different estimates of porosity. An estimated low value of porosity of 0.15, equal to the specific yield of Bill Williams River alluvium as reported by Wolcott et al. (1956), was chosen to yield a low esti mate of travel time. The mean porosity of coarse sand, 0.3 (Bouwer, 1978), was chosen as an estimate of the high value to approximate a high estimate of travel time. Travel time of ground water from the westernmost detonation site (crater 1 in Figure 10) of the multi-charge event to PR1 along the flow line of Figure 10 was computed to be 17.35 days for the lower estimate and 34.70 days for the higher estimate. Travel time of ground water from the southwesternmost detonation site (crater 2 in Figure 11) of the multi-charge event to PR1 was determined from the flow line of Figure 11 to be 18.6 days for the lower estimate and 37.2 days for the higher estimate. Calculated travel times for the two ground-water conditions represented by Figures 10 and 11 show close agreement. The occurrence of the high NO -N concentration 3 of well PRl on March 6, 1979 correlates well with the saturation of the ANFO-affected alluvium during the first or second week of February 1979 in the vicinity of the multi-charge detonation. Travel time calculations tend to indicate further that the high NO3-N concentration of PRl 67 AMS reg F c “MS resP+l By comparing Fc to F^, it can be determined if the differ ence in sums of squares is statistically significant or not. After having applied both tests to the results, the most statistically significant model was used for the analysis of the geochemical data. It is known or assumed that the area of influence from a stream sediment sample is the drainage basin upstream from the sample location. Also it is known that the sample is probably not taken in the middle of its area of influence and that the drainage basin has an irregular shape. If these data were to be coded and fed to a com puter, the computer would assign to each sample an area of influence defined by half the distance to the next sample in any direction. The results from this analysis could be misleading because the drainage basin and the area of influence assigned by the computer to each sample are not the same. To solve this problem, the sampled area was divided into cells of one square kilometer and the drainage basin of each sample was determined. By overlaying the two maps, a weighted value can be assigned to each cell and this value will reflect all the values on the cell along with the percentage of their drainage basins in that cell (Fig. 13, in pocket). Having determined a weighted value 68 for each cell, the data were coded and fed to a computer to be analyzed. All the cells that had a sampled drainage were given a metal value, but only part of the sampled area was used for the final analysis. There were two main reasons for this decision. One is that there were too many empty cells between those cells with a weighted value; the other reason is that there were samples that had very large drainage basins which were of no particular interest and if included, the samples would have a large influence on the trend. Stream Sediment Survey Analysis of Molybdenum Values. The trend in molyb denum values of the stream sediment samples of area A (Fig. 13) is not statistically significant. But when area B, which is slightly smaller than area A, was analyzed, it gave a statistically significant first-degree equation. 2 The R was 0.08, which means that only 8 percent of the variation is explained by this equation, and even though it is statistically significant, the trend is not very robust. The trend surface map shows a general trend to the south east, which is of a very low intensity (Fig. 14). When the regional trend is removed, the plot of the first-degree molybdenum residuals have several areas of interest (Fig. 15). Because the trend surface map has the 69 nn i»4if$n o> jsc fiiu o« ~C»«rOultO tuff4CI iiSMS f-$ciu is wiericu > $?;i8ttcr!K?tere7: 0 iZ14SSTSt I 234>#?ie IZ>***T»4 U » 4>^iS4 IZ>4>»T#4 IZ14SAT## U 14»4TM4 IZ>4$4>S4 IZ>»»47§4 IZ 14$47#4 1Z14$S7M 444A4444A444*Si ^▲1444 4 4044 4444^ 444444444444444 444444444444441I4444444444444S 144444444444441 ■ULi 44444444444444- 44444444444 44444 J l i r 4144414444444444 4444444444444444 __444444444444444L- 4144444444444444 Jiiiiiiiir 4414*44441444444 4441444444444 4JL444444A4444 4 44441441141444 444444444444444 _ _ 4 4 4 A 4 A A 444A4 A A 4. 444144*44441141 aHiiiiilF 44*4*444*444444 444444444444444 iiiiiiiiliiU lL , _ j L 4 A 4444 AAA AA4JUL 4444444444441*4 i i i ? 444444444444444 444444144444444 1444444 4441444^- -HilllllllF' 14444*44144444 i iLl?. p 44444*4444*44444 4444444*44*44444 tl'iiiliriliP1 .▲44* 444 4 44 A AAA 4 A _ P | l 44444444*44444414444**444444 1444444444444444 444444444441444 -▲ 4A4-44 40JI4 444 44 - * 4 4 4 4 4 44 4 4 44 4 4 44 4 4 44 4 4 44 44444 ' iiill—ill niSiSiiiSillll^ 4444444444441 •••••••••••« 44444444*444444 ▲4441414 44 4 44JL4— lianiiliisjiL *4414*44444444 444444444444444 DOOdOOCOOOOC " l l b i i i 444444444444444 •••••••••••••• 44 44 44 44 444444444444 4*44 44 4 444444444444444 4444414444*4444 .siiilll .. 14 4 4 4 4 4 4 4 4 4 4 4 4 4 - .iiill liiliiiiiiiliiL 44444444*414444444444444444 »**#»»*****«»#» 4444411444444444 44**144444444444 lilii Simiiill!! ______44414144*4444444 ____ 44441444*1411141 *444444**4444*44 44 4 4 . 44444444144 .444444441444144 —m P 444*4*14444444* l r 1444444444444*4 OOOOOOCOOOCOCDDO 44*444*44444444 oooooc: p c o o : ocoo _ _ 1 A 44 4 4 4 *4 4 4 444A _ _ 4444441444*44*1 IS—M . 5 7 44*444444*4*444 sIHEIEE"---- "nt 144444444444444 oocsroopecnooi 0 4 4 ll? ) ,*4414*444441444 4 4 4 4* 4 44 4 4 1 4 4* O l3j,S> 11*4 1 1 * 4114*141 d»Zl.|4 444444444444444 >0415.71 14444*444444444 .> 0 & 0 7 .1 S ____AA4444444 444A A 4A „ ►ton l3s23lJO 4444444444444444^ eoooooooooocooo >C7e1.4) 444*444444444444 OOOOOOOOCOOCOOC itiiUiitiiiitt^--- ■li >075*.71 *444444*4444*44 0 JOOOOOOOCOjOOO 13 305 500 >0>4..ll 44444**4*14444 10> .5 7 4414 1 4 *4 4 4 4 1 * >0730.00 4*44414*4*44 ll >05/1.*3 4441444444* 090300000000000 immi!lll n it 00000000003000 » - • • • • » • X* 4* UL1 i8UZ:szLilt«!iA4A10*15.71 44 4 4 444 — »8$E?l3sl!Ei >04*7.1* 4444444 00000009000C0030 30455.57 4*4444 i i i e u r isi!:n 000000000076000 0000000000000900 ■ir - ■ I M F ' 0 3000009300006JOOOOOOOOOOOOO 000000000000000 -sEEIEF- 1 " 000000000000 3 3C 111?;!! " . p P i f W i l l i ------>0251*4) ••••••••••••••• OOC00036009900360000000000000000 OCC C 0 9"> 0 0C 3vO 0 0 O 0 O 0 O O O O ODO 0000:30033030000 .iiiilililif Si!! ooo; do?o;: 3oooo°C lulitliiHulil J i i i r ------O l I J i l k J i t U t i o m . L Z J O . r e 4 ^ . Z J 1 3 . 2 iS _ m k S M » .9 _ lL lk 5 6 T A 3 . L : j. S . > * A _ lZ l* A * T » 3 _ lZ l* l* T ir . .lZ l. > » 2 M _ J U U » T ll_ Fig. 14. Molybdenum trend surface map from the stream sediment survey 70 *0 •Hairs IS O' SSC Oil* 0* O’OOt'i •Viol o* Fj*s»-en.YH tisiOiMis • ;OTTlac u n its ------"r? R — _1--St-*U_LS_XEJLIU>1 • ItSaSSTM W»*»at»« iZSHSfcte* Ula»*»M UlaSfctM W)aS»T«« tZS«t»7M tZl»»*7M lZ>a>*7*« %:»•»»7#* •no? 4 C restorT 3 SOS soo •mi - n r * Om*»«7t* l»»*»*7»* iz»•»»?#» lZl*M*t* lZ»tS*7M 1Z>H>«?0« niaS»7*« )Z)«>»7«« 1ZW07S1 >Z>a>»7»* lZ>»»»7t« CONTOUR LINE 10 CONTOUR INTERVAL • RANCH 4 HILLCREST Fig. 15. Molybdenum residuals from the stream sediment survey 71 lowest values in the northwest corner, this area is shown as an area of positive residuals; but it is of no interest, because of the low geochemical values in the same area. There are also two more areas of positive residuals in the central portion of the area of analysis, and both of them have corresponding areas of high geochemical values (Fig. 16). The area south of Rancho la Cienega has two cells with 85 and 79 ppm molybdenum, and probably most of the metal comes from a thick quartz vein. The area on Cerro Creston is slightly bigger than the other area, and it has cells with metal values up to 114 ppm molybdenum. This area defines fairly well the Creston ridge. Knowing that the average molybdenum content in igneous and sedimentary rocks is between 1 to 2 ppm these two areas can be consid ered anomalous and require further studies to determine their economic potential. The area south of Rancho la Cienega can be given the lowest priority. Analysis of the Copper Values. It was found that a third-degree surface map (Fig. 17) is the most statisti cally significant equation for the copper values with an 2 R = 0.42. This means that 42 percent of the variation in copper values is explained by the equation. The trend sur face map shows a well-defined trend to high values to the southeast, with an east-west elongate dome close to Cerro Creston. The map also shows a saddle south of Rancho el 72 X. AMI i >1 u. l » t 6 » l» l ' WW n it o i m v i x a i o a i* ii»C bc*nii*nti ***Muriu«;ru‘x"»1 t •■ * n?*0.«A)0CCJiivtv.vojooo "iM'-i*UMAUX 1i • %<«>.).non>OZ»3.0000»w06'- »LCII«C »*kUi» **«§ «t«» 'tilT|»kl»V 1» * F1CIC* Cl 10 IC 1*1 1 *0*1* •* * At vi * i »t *ii **iti i f>tAU U 0**11141 Wli**»»»0' llHOele* 1 0 0 *41*1 UHOOMO 1Z>4 00*04 1 0 0 *1** 1 0 4 0 *7** 111*00*** 1 0 4 0 4 *0* 1040***0 1 0 4 0 **0* / Sl/OO.WV *1W *10 *40 * 00 * 00 *10 *10 *10 1 .** .** *,* ♦10 ititiZeAI l S a A eili Resbolodero nwiv.ev ia 3 310 5 0 0 ■ giifili kill SI |i:^ B - IlBil! m m - 3 3 0 5 5 0 0 1i»**j.i* 1 " ' " JV*t*.reEilih *|C 1 1 1 111 - SlisiSj MIX 0 1 0 **4 *"* 1/>«>A*« < 1/ 0*04*** 1*0*04 M* 1**404*** 1 0 *04*4* 1 0 **4*** 1* *41»**» 1**400*10 0* 000**11 : *040**11 CONTOUR LINE 10 CONTOUR INTERVAL ■ RANCH A HILLCREST Fig. 16. Plot of molybdenum values from the stream sediment survey 73 «.*• *:«At I » l » S5C )• 1 * l#r Uwa • CMHt^kii-mo^TFrimcmct-- » ta m M 6 klM T i §f- a.o»? » itcuf »f,un t*tC»ll 1$ f«*TICU 4 » • in«>»Ti« u i »$ » 7 m i z » *> s t *« u »« i * 7 » * u h > * 7 m u > « » *7 *« ...... — Son Jeronim o ...... — .,:!!!rn ^TiF ■!i:]!!P. . I4AA m# il|iE«!i!!t!8iR...... r.: T H = ------i . -illliiiHi I #% jiiiii!liiHiiHiniiiii!!iHiii!!iHliih; 1111 1 | ------iiiil«iiliiiiiMiilii|iiiliiiiiiiijilii!lihii.,— -lifer- y j l l i P " ' .. sia2i!!Sli!!!i«! 3 310 300 ------nnrfitK tiM M iiittitttttit'.riT iT T - SAAAAAAAAA4AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA . ii!xnTrrArinAiliAAi4f**iA4t4-"fi"444A44uriiiii^iAiliiAi Bill ..iE»l»“ 3 ^ 4 )6 . 67 S I M I M I. 1AAAA AAAAA AAA •••••••••••••••••••••»•••••••••••••••»••»•••••••#••••••••••• *»#»»####***»##*#*»*#** *»*##»##****»*##»**#**« i* ••••••••••••••••••• ***»*#*»****#»##*# » > * * * •-M-W - l i h i F eooToocjoooooooooooo cicogeco^coooeeoeee 000300000JOODOODOO oooeaooooooooooop____ r.':--— ,.,mmi!;inFsss- I l H i i l - ,« ooccoouoooooou: IliL I l i i K , ,Ii 00000000060 OOOOOOOOOVO 3 305 5 0 0 E aiW 00 00 09 00 ^iS§jS^5?Sgg5S§%^Uo,oooooo^JOU JJUOOI ------n m - r r m — • •4**l«**ttl*W ***l I l L 411*1*«4S*«*4 — 1ll*111«rST1TKTTT^-- j_lZM7*7*l 127 )07** i;i»7tT0* Fig. 17. Copper trend surface map from the stream sediment survey 74 Huerigo, and there is also a slight increase in copper values toward the San Jeronimo area. The residual plot (Fig. 18) shows three areas of positive residuals, but the area across the northern part of the map is of no interest because the geochemical values in that area are less than 50 ppm of copper. The other two areas occur in the southern half of the map, and they are only separated by a small zone of negative residuals. The two areas have corresponding areas of high geochemical values. Since the average copper content of igneous rocks is 70 ppm (Hawkes and Webb, 1962, p. 364), the cells of copper content higher than 100 ppm were outlined. The area on the west part of the map has only two cells with copper values in the 200 ppm range; again as with the molybdenum values in that area, the quartz veins appear to be respon sible for the copper values in those cells. The residual plot and the plot of the geochemical values agree that the highest copper values are on the south side of the Creston ridge. The cells with the high values determine the domal character of the trend surface map (Fig. 19). After analyzing the surface maps from each survey, a comparison between the copper and molybdenum results was done to see if there was any particular relationship between these two elements that would be of interest. Even though the copper and molybdenum surface maps are of different degrees, both maps show a general trend CU AHAlVSi; 5« SiC »AlA U* 75 nr; ,ir Qr-THm^mrrfrmuia------:ii{^;VS"--ji{?gr§§ggfj— gj^jg ^ -: - iins^ r — • VOiTEO VALUES nave »E>n "UlTIalIIO AT a EACTDa 0* 10 TO IwE jWTioioO**'*io.»T*E I ISLaLI »4LUI> . J ilt ALL-LL-XLLLLLAL 1*MA»A« XZ1ASA7AA IZSASATO* li»A$AW IZ>«>ATA« IZSASATAV 1Z1ASATAA 1Z»*»ATA« 1I1A1ATSA »4?l». »<1>> >tl«L e Huerigo ~ 3 310 500 TIT Aiee Creston \ Atei ______iSXi______»ZOT ♦!?> AZA? « J La EOA »ETi 01E1A AeTAA lMA»er«A lZl*»A»e« iz>a«ataa szs ava taa IZAaSATA* IZIAAaTM iziasatwa IZLAlATiA IZ*A»»TM 1Z SAL A TEA I .— . CONTOUR LINE # RANCH SO CONTOUR INTERVAL A HILLCREST Fig. 18. Copper residuals from the stream sediment survey 76 t v ifcst f *11 or H i 3*11 r» ►iiif ct o»e*i* «i»cr.ieti«uiin **i 11'*'** I 1 i*iii.e»i S l i p •»eo •z»e ’illiiii Huerigo 4ZM.&* •Zt» Z*0 •toe •too •zoo eiro ezoo 1!: lull).* iiie ih iliiiiii • l i t • 1*0 ♦110 «05 to 1! •100 •100 •zoo •too •ZSC •Z10 zoo 6 $U:i> Eill •110 •110 *Z0 •Z10 ZOO •Z10 •1*0 1*0 rJB: liiiisi m?5:V IEI ill Bl i ’ ho'.oo 3 505 500 IL:V: IIP pill E t i i Z \ 1 1 1 • il«ox •100 •10" •101 •no •1*0 •no e illile ts * IZ**»*t*< IZ»»1M»« 111* 1* 1,* U H » * 1«0 lll* » 1t** 111*1* 1** 12!**»!** 12>*>*1«* IZ1* 1*»M IZ**»**#1 ___ CONTOUR LINE ■ RANCH 100 CONTOUR INTERVAL 4 Ml LUCRES T Fig. 19. Plot of copper values from stream sediment survey 77 in a southeastern direction. The trend is defined by the high geochemical values close to Cerro Creston. The copper surface map being of higher order gives more detail than the molybdenum surface map. There is a general 5 to 1, copper-to-molybdenum ratio noticed in the intensity of the trend surface maps. The residual plot and the plot of the original data show that the areas across the central portion of the map are of interest; the areas of high values for copper and molybdenum have different shapes. The plot of the molyb denum values define very well the Creston ridge, while the plot of copper values shows that the higher concentrations of copper are south and southwest of the Creston ridge. South of Rancho la Cienega, both metals show the same area of interest. The geochemical values have the same general copper-to-molybdenum ratio as the trend surface maps. Rock Chip Survey In addition to the other reconnaissance survey done over the Opodepe mining area, a detailed rock chip survey was done on Creston ridge. The purpose of this survey was to help evaluate the area of known mineralization. In this study, the rock chip survey will be included and used as a control area to help analyze the results from the other survey. The survey lines were originally intended to be 78 on a north-south direction, but due to a grid error, the lines came out to have a N. 28° W. orientation (Fig. 12). To handle the data better, the coordinates were arbitrarily assigned to these samples but the survey lines can be easily incorporated to any topographic map. Analysis of Molybdenum Values. The results from the analysis of molybdenum values show that a fifth-degree equation is the most statistically significant one, and it 2 has an R =0.27. The trend in this area is defined by a dome to the west of Cerro Creston, and a N. 28° W.-oriented saddle at the western edge of the Creston ridge (Fig. 20). Due to the lack of data to the north and south of the map, the information shown on those areas is not reliable. The residual plot (Fig. 21) has several areas of positive residuals, but only the ones on the eastern por tion of the ridge require further studies. Where there are positive residuals in the eastern portion of the Creston ridge, there are also high geochemical values. In the plot of geochemical values (Fig. 22), the area of molybde num content greater than 100 ppm has a general northeast direction. These high values determine the domal character of the trend, and it is very conclusive that molybdenum is restricted to the eastern portion of this ridge. Analysis of the Copper Values. Copper gives only a second-degree statistically significant equation, with a mi A iu tru\ III I»C li*l* VI m im n n m i m . m i 111 iu - m .u f i i n u n I MU l t h i l l llAllKUh * « \ '»00 . 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HI III ll ll It ilMO I Ill'll I'M ******************************************* 7 l / v . v o III OMMlIIhllllliBOH **************************************** o o o 0 0 '1 I I t 1 1 1 1 11 I 1 1 I I ° o . ' / » / . ' / Hill'll lie-I HO'I II nil HO 7 7 I! It Ml 01! 0II0 r II !• 0II h H O O T , , 1 1 7 7 " I , .’ / / / . O h HHi Fig 20. Molybdenum trend surface map from the rock chip survey to 1.J Af.Al T» IS HI HI llA l A III I MIUI Mi n o r m 111 i i i - d i i h 11 m sioi*Li Pl011 Hit i IM Il m K iron a • i«.oo.ouoooo him mim k loon.oooooo «a a | nun v • 30CO.COOOOO himmiH v l? 0 0 . 01:0 ore !-v*iU l'ioov!o(''!"]2.im i x i>C»ti VAUI1 Y-kC*ll IS VtHl HAl Ul »1S1AI./W# IflMttl't Ifltiovm v U)SS67a<< If 14167** lZ»S>fc70'#/l2Ht.h719 I73ki67«0 I7HS67»9 1/14,40749 17 IS 57 749 lOild.OO • I" ♦ 1 / -5 1 -7S -19 19 /97 i i,l/./s 7 . 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I 9 9 *. . 1 9 • 99 • 190 • 210 : ? r • 160 m .’: 5 1 % ♦ 220 1 1 *1 .0 3 :! u : :?fs 1*0 • 120 • 141 II i; 140 • 900 »? 70 ♦ i l i • 20,1 • 470 • 120 t i r o t i l ♦ 111 ♦ 47 MO I .911 • Z • 7 ♦ 49 x ?° :s?8 • 490 :M3 tv s • 12*. «% 110 i l p •71 • 260 tic 0 • 111. • 4 ♦ 400 •400 U ;T ♦ 190 i l l 1 •149 tnso : l v (.4i,.UV • 410 6 0 7 .1 2 11,9 • 790 ♦ 230 • 710 • 640 • 290 ♦ 106 * IU*» ♦ •» 4« | 0 t i L • 290 3 1 0 . 4 * • 140 • 2*.il :j!5 III! i i l ? i l l . 47 1 .1 0 ♦ 230 ♦67 fz : v :i?8 •4 • 340 • / in • 2 200 i f ! • 4 • 4 310.43 VI • A I S 9 . 3 7 : r 121(1 • ♦20 ♦1 U'ni; • 4 4 ♦ 2200 • 7 • 0 • 360 t.U • 4 • 1" • 4 3 • 10 ii" • 42 0121436 709 121456 719 123436/19 I,11431.719 1/3436799 123436719 1/1446/91 121456719 1/1447.799 121456799 12145(79 Fig. 22 plot of molybdenum values from the rock chip survey 82 goodness of fit of only 8 percent. The trend surface map defines the Creston ridge as a saddle of low copper content and there is an increase of metal value to the north and south. Even though there is not enough data to the south to give full confidence to the results, the general trend can be appreciated (Fig. 23). The residual plot (Fig. 24) shows several zones of positive residuals scattered throughout the area of analy sis. In Figures 24 and 25, the plot of geochemical values, along with the residual plot emphasized that there are higher concentrations of copper on the south side of the Cr.eston ridge, with some scattered values on the north side. From the analysis of these two elements, several conclusions can be made about their chemical distribution. The intensity and amount of detail shown by the two trend surface maps (Figs. 20 and 23) is not the same, but at a general level a good comparison can be made. From the molybdenum trend surface map it can be seen that the trend is defined by a dome close to Cerro Creston and the plot of geochemical data shows that molybdenum is restricted to the eastern portion of the Creston ridge. From the copper maps it can be seen that copper is not restricted to the eastern portion of the Creston ridge. On the eastern half of the ridge, the copper-to-molybdenum ratio is less or equal to 1; on the western half, the ratio is greater than or equal Ml Afl*lV>| . I ' At i.Al A l|l II, IWU « I iiwiDui'H' iicivm-iH••.Hir \unF»ce m i l I Ml'. HIM is riximn x • ^'.in.uiooou n i.it him x • KAXIMJ.I V M l'JV .I.OdllOVU MininiiM v . I W : ?) ™ )03VU 00 X-SC*Ll l\ MUSIfIN 1*1 *-V*lUI • tHUP.OH I inio t ISCAU viiur i v-'.r ALv I < V IM |t*l CUUI DIN I Ilf I *• V *1 • I o . o j l- H I VI uc I r oil 11.|» I ...... | . 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" " Illlu444St4t " 1311)11 u v tv v tv | 4 | • . 3.1 6,..f 5'%5''*5 444454 1111)3 in I'OHf'O0000 I 3 0 . 4 5 *-‘.6»*.6 555555 444444 1111.1) I 149. 7 73 V.-.nl.A, /••35S5 444444 77777 9# Phi 55*91, 4-4444 j ' ^ ' ^ l l n , ".C.HUOOU S! IJ.1 i 777 77 fc^ri#,bh 54554 444445 H I D I 2222722 0OHIO 9 0 0 0 4 0 IHHM 7 77 7 7 V-hSS 55555 444444 3) 1*31 in. OOUOUOC . 3 5 »■••• »•• 7 7777 61,4626 55999) 4444*4 333)3 I "111 OOOPPOO ® 4 4 4 4 4 4 M n i . s l 9»'*•#'. 7 7 7 7 7 i.4 S, 4 •.•55 5 5 5 „ „ , r w ? 7 2 2 2 2 7 M l u ropoon 312*4 4799 1 :3444 73# Iil4 5l79'# 17 145,74 1 123456789 12 14,6799 12145* 76# IZ 34547M" 17)455789 |2 145478" 17 1446 789 CD Fig. 23. Copper trend surface map from the rock chip survey U) I II A t« «l V «I • III » I. IM • A "I li ' IVl I I ••i'll woo.no -»ul • Sill - 1 1> 1 - l II '1 . 7 . - > 0 l i V I I't I - . ' l I I 7 K f .111» -S f - •If flit).SI III i l l : ? n —f f 4 *iO >I/,| -III. 144 - I t l • f l -2 0 4 /771.M -H 2740. 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' "I ->‘»l :?{? 21 s,i. in -1 1 4 * f 6 f - J * 4 -2 • 1 firs.it y -4S> ->.•0 • 6"64 - l, i> - J l l -20V - Al'4 :HI -1 6 4 fO ',0 . 1'. - 1 / 4 <1741 - s v -I f 6 i ) i i fuM'.'l • f i l l - T f * i l l : 1 - f to : h , i l l 1 i I I V I - . l I I'll J. i* 1 * 4 40 -JO -SO.! : f « -1,1 > ♦ 81 -7 4 -2 4 0 T. a n - US'MS : ; x -1,4 1 H i1 : $ I 3 -2 7 1 -HO) :?V -71.1 -4 0 -1 4 2 ♦ J14 -14 • 4 - 2 > r 221 -134 -PA -IOOJ -/•»*, -361 I ml. «o • 310 * :%? -304 l / 1 v . v f : s ; i -70S 1 7 ) 7 . 1 4 - v i 5 II 1 104 . ft, — 1 ) 4 I i l l ? » !• i l l ! : i ! l i l l s ' I, 7 7 . I i - IS 7 MSC. )0 -444 - 4 f l - f ? J - I 0 f 4 • 11S4 - t 4 5 - 1 4 " -4 J0 - M 1 -•IS -1 4 4 H S l * :IT -4 4 4 a a : ! { ' ( i i i ! IK li’vli -OlO • / • . i f • 1 v74 -7 7 3 -4 4 4 -1 6 1 ♦ 1 S 4 • 376 #4*7 - i * i « F |A 4S . I I -1 1 1 4 -10 4 0 # 2 , m :W i l l : - i l l ? -e7ii -10 3 7 -1 1 7 -160 74 -6 4 0 ♦ i n i -144 -4 0 4 - • 4 * -1161 • 7 (1 • 731 l/lv.OSI;:;::', -42 7 -4 7 6 i l l ] • 611 -rtF* O tf »4‘»I »•") If ISS471I U «4'.r 7.1 • lf|4V .7s» 1/«4S<,74'| |f 14 >1,7 4* I2 14S67MI |fJ4 >1,740 If lAtAfhO lfl4SI,7f«> |?t4>'.7-,'» Fig. 24. Copper residuals from the rock chip survey 034^ in ANAivsi* i«i »•; i « * i * hi urum v t PI III 'll ||KH.|I«AI DATA l/-CII!IW !l|ll»ll SI run r vv. 11 u is MAXIMUM X • SA'JV.VCOvUll r.iu i mn x 1000.000000 MAXI H'M r I lO'ii'.oovoii'i rIM|MillrIM|(HIM v v • iroo.oooiiou 1*1111 ItU V A lU f S IIA VI M trn M U l T IM l iD MY A Y AC TU* OF 10 Til lilt 1 FllWtt 5-viiuSi !sir:r!%.Y-.o x iscau vauiu r--,t Alt 15 VI FT If Ai Ol.*JA*.» T-X-I 1?YAS|.7 im 17 14'Afnu 171A>6Tn'l |?3A>67MO lf34»A7|.'l |7)AyM7"9 lM A,M7nq 1*14467*9 l*]'.,67**9 JIlUO.OO til * 740 » 100 *400 • 440 *4 00 • ZO'I • /to o ?:> M. 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I" • too • ion : f $ :L • 47*0 • ‘ 00 1 4 4 ,. . 1 , • 4440 ♦ «5n MRS : > i r m • 1450 E • 1 100 :B • H f •HI" ivo iis s \ m ♦ TOO i l l ! : 1*00 ♦ 1750 •90 l ? l o . 4 * •603 ♦ 4003 • **5 0 • 140 *00 1478.10 • 4500 • COO ♦409 ♦ 4310 • 640 :'SR *1.50 • 6«»M0 :css m :s?2 •100 !s s : i 41 ♦ • i i 4100 • t5ti ♦700 Wllu • 35 0 I MV. 14 •1*0 • 700 1150 • 4VV KS !? (n • 7'.0 6 50 . 1*440 *90 • 1500 1000 4*tO Itv II • 450 • MOV 900 4 1 7 CP ivo ui .’.I4*.r 7 If l.M'44..7l » 1*14 »7 I * T .M 4'"7 ho 1*144079 A I.- 1446799 1? 3441.71 9 1,34447"* I* 14««.7I'M |*|41',7"9 1*14447*9 Fig. 25. Plot of copper values from the rock chip survey 86 to 10. It would be very interesting to correlate the areas of high positive residuals and high geochemical values of both copper and molybdenum to any drilling done in this area. This would show how well the surface values corre late to subsurface values, and maybe help plan any drill sites. Comparison of the Different Surveys At this point, it will be of interest to compare all the trend surface maps for each element and see how the element behaves in each survey. This will be a generalized comparison, because not all the surface maps are of the same order or have the same intensity. Molybdenum Trend Surface Maps. The stream sediment trend surface maps give a trend to the southeast, which is defined by the values around Cerro Creston. This trend is corroborated by the trend in the rock chip survey on 2 Creston ridge. The rock chip survey has the highest R and the stream sediment survey the lowest. The residual plots and the plots of the geochemical values show similar areas of interest. Here, again, the area of high molybdenum values of the stream sediment sam ples are in concordance with the area outline by the rock chip survey; both surveys outline the Creston ridge very well. The only area of possible interest shown by the stream sediment samples is south of Rancho la Cienega. 87 Copper Trend Surface Maps. The copper trend surface maps are approximately of the same degree and intensity; this will permit a better comparison than with the molybde num surface maps. The trend over the whole area is defined by the stream sediment samples as a dome with an east-west axis on the south side of Creston ridge. The rock chip survey has very little data for correlation and only sup ports the dome and higher values to the south of Creston ridge, but very vaguely. The trend from the stream sedi- 2 ment survey shows the highest R and the trend from the rock chip survey the lowest. The residual plots and the plots of the original . data of the stream sediment survey show only two zones with anomalous copper concentrations. One of these areas is southwest of Creston ridge, and the other one is around Rancho la Cienega. CONCLUSIONS AND RECOMMENDATIONS The oldest rock in the area of study is a mixture of gneisses and mafic rocks. The gneisses have a east- northeast textural trend which appears to be characteristic of the Precambrian rocks. Overlying these gneisses are a series of quartzitic beds. Even though there have been only epeirogenic movements from the Paleozoic through late in the Mesozoic era, the only record left from that period of time is the quartzite beds. The Laramide orogeny started at the end of the Cretaceous period and ended early in Eocene time. This orogeny caused major faulting and very tight folding as suggested by the quartzitic remnants. Also during this orogeny, several felsic intrusions along with rhyolitic and dioritic dikes were emplaced. The major structural features caused by this diastrophic event have a northwest direction, which was particularly noted when mapping the sedimentary sequence. After a period of erosion, another diastrophic event started late in the Eocene Epoch. This event, known as the Basin and Range orogeny, caused strong normal fault ing, and produce the horst and grabens characteristic of this region. The structures have a general N. 0°-10e W. orientation, and one of these regional faults partially defines the San Miguel River. 88 89 The aerial photographs were very useful, especially during the field work. In the field the photographs were used as base maps, and all the geologic information was recorded on acetate overlays. Also, when the photographic characteristics of the different rocks were known, the field work was done faster. During the photogeologic interpreta tion, the color aerial photographs were most useful. The geochemical program carried out in the area consisted of a reconnaissance stream sediment survey and a detail rock chip survey done on Creston ridge. To analyze these data, a trend surface analysis was used. From the results of the rock chip samples, it can be concluded that molybdenum is restricted to Cerro Creston, and there are more high molybdenum values on the south slope than on the north slope of this hill. Copper is not restricted to the eastern portion of Creston ridge, but it is mostly concen trated in the southern slopes of this ridge. Because the reconnaissance survey and the detail survey map are at different scales, it is very difficult to make a good comparison between them. In a general way, it can be observed that the results from the stream sediment survey show a good correlation with the results of the rock chip survey, and outline well Creston ridge. The surface maps for copper and molybdenum from the regional survey show generally southeast trends, and the residuals 90 and the original geochemical values generally outline the same areas of interest. In the study done around the area mapped by Minera Opodepe, no areas were found with the alteration intensity or mineral expression similar to Creston ridge. Only small workings were found during the field work. These workings appear to follow isolated quartz veins. Even though the zone around Rancho la Cienega does not show a high molybdenum or copper content, west of this ranch there is a strong vein system cutting through the Sonoran granite. The quartz veins appear to be fairly abundant, and in some of the veins minor amounts of pyrite with lesser amounts of chalcopyrite and molybdenite were recognized. The vein system is very noticeable in the aerial photographs, and the veins have a general east-west orientation. This area needs more geologic mapping, and special attention should be placed on the density and orientation of the veins. Along with the mapping, rock . chip samples should be taken and analyzed for molybdenum, copper, silver, and gold. I APPENDIX STATISTICAL CALCULATIONS FOR THE TREND SURFACE MAPS 91 no a n a l y s i s or ssc d a ta of opodcfe COEFFICIENTS OF FIRST-DEGREE EQUATION Z . -330.29963 + .01520 X ♦ -.01452 T ERROR MEASURES SURFACE FIRST-DEGREE SECOND-DEGREE THIRD-DEGREE FOURTH-DEGREE FIFTH-OECRET SISTW-OECPEE STANDARD DEVIATION = S 20.57 0.00 0.00 0,00 0.00 0.00 H “!IS«2?it" tM "'0=ssreg • 31712666E *04. 0. 0. 0. 0. 0. « 'i“ «"*ssres . 16799597E405 0. 0. 0. 0. 0. I0IA1 VAKlA-UtlN : S S f Ai.l9.9JO864Et0a 0# 0. 0. 0, ss'.EEHiiinoa5 = r 2 .07933946 O.ODOOOODD 0.00000000 0.00000000 0.00000000 0.00000000 ^ i E r . ! f 3 1 °r =R .21167260 D.DDDODOOD 0.00000000 0.00000000 0.00000000 0.00000000 CU ANALYSIS OF SSC DATA OF OPOOEPE COkTFlCIERTS OF FIRST-DEGREE EOWATfON l • I72z.eb0>l A .00217 X «■ -.05767 1 C OErFTC I E NTS OF SECOHCT-OEGRFE' EOITATTON t * -274361.32301 ♦ 7.03201 X ♦ 6.09062 V ♦ -.00006 X2 4 -.00001 XY 4 -.00009 Y2 COEFFICIENTS OF TTirRU-OECRfE EOVATION" .01592 XY -.06267 Y2 4 1 ■ -i!8?l§!-iV52 * -.Uiil'li'y! * iililli'i,! : :8888$ H 1 ERROR MEASURES SURFACE FIRST-DECREE SECOND-DEGREE THIRD-DEGREE FOURTH-DEGREE HFTH-DEOREE SISTM-OEGREE o o STANDARD OEVIATION=S AS.56 63,61 38,39 0.00 0 .0 0 o 8{"!5!18i,.i,,“ ",“,=ssr.g .77090959E»05 .125603776406 0 . 0 . 0. 8f!5S(°c!M“r » '“ -"=«=ssr, s ,215559626*06 .160066616406 P. 0. Pf TOTAL VARIATTUIteSSt .273650301706 .273630361706 .79T6303GE10P 0. 0 . P. SfStrSHJSf[nSf=R2 .26563166 .62736236 o.ooooonoo 0.00000000 0,00000000 cSSIEl u SSJ °r=R ,51520039 .65371626 0#00000000 0.00000000 0*00000000 t£> W Ml) ANALYSIS Ot KC D M A Ul OFODlrFE CUCFfICILNIS OF FIRSI-OECFEE EOUAilON Z • 119.33506 ♦ .07453 X * -.09703 Y COEFHCIENIS OF SECONO-OEGKEF. EQUATION r- 0 c 1 i • -19C6.54223 $ .42450 X ♦ 1.30624 Y 4 .00002 X? 4 -.0001? XY ♦ Y2 CUIFF HI INIS OF INI RU-DlGRl E I QUA II ON t o Z " -1571.59097 ♦ -.54264 X + 2.40199 Y 4 .0002? %2 # .00023 XY 4 o Y? 4 -.00000 X3 ♦ .00000 X2Y » .00000 XT2 4 •00000 Y 3 COEFFICIENT OF fOURiM-OECREE EQUATION l • — 12 724.05296 ♦ m.26545 X ♦ 11.00351 Y 4 -.00701 XY .4 -.00266 Y2 4 .00000 X3 4 .00000 X2Y •« .00000 XY2 4 ::88ooo H : —.00000 X4 4 .00000 X3Y 4 -.00000 X2Y2 4 -.00000 XY3 4 .1)0000 Y 4 CULFFICILNIS OF FIFTH-DEGREE EQUATION 1 o / • -34011.51570 4 -13.62323 X 4 91.41101 Y 4 .0128$ X2 t -.00346 XY ♦ o Y? 4 -.00000 X| 4 -.00001 X2Y 4 •00001 XY2 4 .00003 ri ♦ „ .00000 X4 4 ,00000 X3Y 4 .00000 >?Y2 4 -.00000 XY3 4 -.00000 Y4 ♦ -.00000 X5 ♦ .00000 X4Y 4 -.00000 X3Y2 -.00000 X?Y3 4 .00000 XY4 4, .00000 Y5 ERROR MEASURES iVFFACl FIRtT-OECRtt SECOND-DECREE THIRD-DECREE FOURTH-DECREE FIFTH-DECREE SIS7M-DFCRF6 STANDARD DEVIATION = S 251.86 24m.10 241.07 235.19 231.65 0.00 SJ'!S!;Kt‘,,“ ""°=ssreg .A7$09912C«07 •564026391407 726780886407 .859154506407 .937168722*07 0. sruj/sEk"01 ‘>'i“ "=°=ssr. 5 . 3000A367E*08 ,29115094:408 27487549E408 .261638136408 .233dl671E»08 0. IUIAI VAklAllUN=SSt 3475$358E»08 •347553581408 34755358EtOe .347553586408 .36755358EtOB 0. S?SE!HW{uS '= b 2 .13669809 .16228473 .20911334 .24720059 .26970681 0.00000000 SUSSEiSliSJ " = R .3697270$ .40284579 .45728912 .49719271 .51933112 0.00000000 CU ANALYSIS OF PC DATA OF 0P006P£ COEFFICIENTS OF FtPST-OEGHEE EQUATION l • 203.6716* ♦ -.0007* X ♦ -.06220 Y COEFFICIENTS OF SECONO-DEGKEE EQUATION Z • 677.8*270 ♦ -.12**6 X ♦ -.53853 Y ♦ .00000 X2 ♦ .00005 XV * .00006 Y2 ERROR MEASURES SURFACE FIRST-DECREE $ECOND-OEG#El THIRD-DEGREE FOURTH-DEGREE FIFTH-DEGREE SlSTH-OECPEF STANDARD DEVIATION: S 67.*0 66.05 0.00 0.00 0.00 0.00 !}*i!)«K!!s'm *",“ sSSreg .2ll67930E<0b .32221053Ef06 0. 0. 0. 0. iria H iV 0' '” “ '"'"=ssres .36132727E«07 .350274ME407 0. 0. 0. 0. IUIAI VAR 1A II ON: SSj .382*9>20E«07 •l*2^9520Ef07 0. 0. 0. 0. .0553*169 .00423911 0.00000000 0 .00000000 0.00000000 O.OOOOOUOO £ 8 « E i5 !i5 ; “f =R .2362*81* #29023974 0.00000000 0.00000000 .9.00000000 0.00000000 REFERENCES Alvarez, Manuel, Jr., 1966, Geologia, paleografia, y tectonica de Mexico: Unpublished class notes, Universidad Autonoma de Mexico, 200 p. Anderson, Thomas H., and Silver, Leon T., 1973, The Cananea Granite— implications of its Precambrian age (abs): G.S.A. Annual meeting, Dallas, Texas 1973, G.S.A. Abstracts with Programs, v. 5, no. 7, p. 534. Cooper, G. Arthur, and Arellano, Alberta T.V., 1946, Stratigraphy near Caborca, northwest Sonora, Mexico: Am. Assoc. Petroleum Geologists, Bull., v. 30, no. 4, p. 606-619. Damon, P.E., 1968, Application of potassium-argon method to the dating of igneous and metamorphic rocks with the basin ranges of the Southwest, in Titley, S. R.(ed.). Southern Arizona guidebook III: Tucson, Ariz., Arizona Geological Society, p. 7—20. Damon, P. E., Livingston, D. E., and Giletti, B. J., 1962, Extension of the older Precambrian of the south west into Sonora, Mexico: Geol. Soc. America Special Paper 68, p. 158, 159. Damon, P. E., and Mauger, R. L., 1966, Epeirogeny-orogeny viewed from the Basin and Range province: SME Trans., v. 235, p. 99-112. Davis, J. C., 1973, Statistics and data analysis in geology: New York, John Wiley and Sons, Inc., 550 p. De Cserna, Zoltan, 1960, Orogenesis in time and space in Mexico: Geol. Rundschau, v. 50, p. 595-605. Dumble, E. T., 1900, Notes on the geology of Sonora, Mexico: AIME Trans., v. 29, p. 122-152. Eardley, H. J., 1962, Structural geology of North America: New York, Harper and Row, Publishers. 96 97 Fries, Carl, Jr., 1962, Resena de la geologla del estado de Sonora con enfasis en el Paleozoico: Asoc. Hex. Geol. Pet. Bol., v. 14, nos. 11-12, p. 257- 273. Hawkes, H. E., and Webb, J. S., 1962, Geochemistry in mineral exploration: New York, Harper and Bros., 415 p. Imlay, R. W., 1939, Paleographic studies in northeastern Sonora: Geol. Soc. America Bull., v. 50, p. 1723- 1744. King, R. E., 1939, Geological reconnaissance in northern Sierra Madre Occidental of Mexico: Geol. Soc. America Bull., v. 50, p. 1625-1722. Livingston, D. E., 1973, A plate tectonic hypothesis for the genesis of porphyry copper deposits of the southern Basin and Range province: Earth and Planetary Sci. Letters, v. 20, no. 2, p. 171-179. Lodder W., Hursh, J., Lopez, F. L., Miller, C. P., 1975, Summary progress report of Cerro Creston, Opodepe, Sonora, Mexico: Unpublished report, Cia. Minera Opodepe, Hermosillo, Sonora, Mexico. Lowell, M. D. and Guilbert, J. M., 1970, Lateral and verti cal alteration-mineralization zoning in porphyry ore deposits: Economic Geology, v. 65, no. 4, p. 373-408. Maldonado, K. M., 1954, Nomenclatura bibliografica y correlaciones de las formaciones Arqueozoicas y Paleozoicas de Mexico: Asoc. Mex. Geol. Pet. Bol., v. 6 , p. 113-138. Mulchay, R. B., and Velasco, J. R., 1954, Sedimentary rocks at Cananea, Sonora, Mexico, and tentative correlation with the section at Bisbee and Swiss- helm Mountains, Arizona: AIME Trans., v. 199, p. 628-632. O'Leary, M., Lippert, R. H., and Spitz, O. T., 1966, FORTRAN IV and map program for computation and plotting of trend surface for degrees 1 through 6 : Kansas City, Kansas, Kansas State Geological Survey. 98 Ramirez Ruvalcaba, Jose, 1965, Geology of the San Antonio Mountains, State of Sonora, Mexico: Unpublished M.S. Thesis, The University of Arizona. Salas, Guillermo A., 1970, Aerial geology and petrology of the Santa Ana region, northwest Sonora: Soc. Geol. Mex. Bol., v. 31, no. 1, p. 11-63. Solano Rico, Baltazar, 1975, Some geologic and exploration characteristics of porphyry copper deposits in a volcanic environment, Sonora, Mexico: Unpublished M.S. Thesis., The University of Arizona. Taliafierra, N. L., 1933, An occurrence of Upper Cretaceous sediments in northern Sonora, Mexico: Jour. Geology v. 41, p. 12-37. Vasquez Perez, Adalbert©, 1975, Economic geology of the Alamos mining district, Sonora, Mexico: Unpublished M.S. Thesis, The University of Arizona. Wisser, Edward, 1966, The epithermal precious-metal province of northwest Mexico: Nevada Bureau of Mines, Report 13, part C, p. 63-92. L — 97 3 8 1 8 Section LOOK IN G NORTH Section A-A' C-C' I B B 1000 -I - 1000 meters 9 0 0 9 0 0 - - " ^ // u '> II ^ \\ // * \\ «S // 1/ H = ^ '/ ❖ H /, * " // )\ ^ V - 8 0 0 8 0 0 - »/ * * = = ii ^ II = 4 ^ — \\ = // ^ u ^ II ❖ » » _ ii = n % ^ // || \X * v n 7 0 0 - II * n w * - 7 0 0 = // = // ii ^ //" wV f L i \ C H * * f ii u // H « = <> w // II ■=////A " -/— -I '/''Ll - 6 0 0 * ii // ii ii \i = ^ w II ii \' // ^ " / / » \\ a i.o,9; ii \\„ ^ » *■ " I / ^ V x. 5 0 0 - ; = H ii n ^ w H \\ » " \\ -^ II ^ I s / \ \/ \ - " II 1/ f //» H " // \\ * X = " = * // 1/ // w *//||< > -\^0 i1 \\' II v \\fllf *»ll ^* // v\ ❖ ^ 1/ " o >':-a o -c I \X/ II 4 0 0 - n ii ii . " M* « /z ii ii ❖ " » ' V ’ \ - I /X| V " ITV-V'^x /V, - I 7 / X / 3 0 0 - - 3 0 0 W a V 'i /O o O' 2 ,0 0 0 E 3 , 0 0 0 E 4 , 0 0 0 E 5 , 0 0 0 E 6 , 0 0 0 E 7 ,0 0 0 E 9,000 E 10,000 E 11,000 E 12,000 E 1 3 ,0 0 0 E 1 4 ,0 0 0 E EXPLANATION Quaternary -£ jV° 131 a ALLUVIUM AND TALUS BRECCIA ------CONTACT, DASHED WHERE APPROXIMATE ----- FAULT RHYOLITE PORPHYRY Tertiary ( ?) - m 7 m QUARTZ MONZONITE PORPHYRY SONORAN GRANITE SCALE Figure 8 HORIZONTAL VERTI CAL Cambrian (? ) -£ QUARTZITE, SHOWING BEDDING h 10000 1-5000 GEOLOGIC CROSS SECTION B - B* OPODEPE MINING AREA Paleozoic (? ) CRESTON GRANITE and/or SONORA, MEXICO earlier (? ) ANDESITE- DIORITE AUGEN AND BANDED GNEISS JOSE RAMIREZ MUNOZ. MS. THESIS. DEPT OF MIN. AND GEOL. ENG. U. OF A. 1979 2 5 ( r LOOKING WEST S e c t i o n Section EXPLANATION Q uaternary | 0 ° 13 ALLUVIUM AND TALUS BRECCIA P a le o z o ic ! ? ) CRESTON GRANITE INTRUSIVE BRECCIA a n d /o r - earlier (?) ANDESITE - DIORITE ACID TO INTERMEDIATE DIKE ROCKS Tertiary! ? ) - AUGEN AND BANDED GNEISS T 8K ^ QUARTZ - K-FELDSPAR PORPHYRY Figure 9 m m i \ QUARTZ MONZONITE PORPHYRY SCALE GEOLOGIC CROSS SECTION C - C SONORAN GRANITE HORIZONTAL VERTICAL I IOOOO 1=5000 OPODEPE MINING AREA ------CONTACT, DASHED WHERE APPROXIMATE SONORA, MEXICO BEDDING CambrianC?) -£ QUARTZITE, SHOWING ~ ~ F A U L T JOSE RAMIREZ MUNOZ. M S. THESIS. DEPT OF MIN. AND GEOL. ENG . U. OF A.. 1979 /f7f 254- % » -i^V' xv- - f 1 / V « t r '' . I CMUHANf.tlK) ty y < . I ^ ^ • , hM ^UO fO^N CJU DA . - f < • • . ' Lx' > i V/ Y / «w > 4/ f / y* // 1' >' V? »/| *.v • r ' > :/ tl ‘jtf! - - b i z ./ u x ./ -L > v - X ii Om \ *a AtKHdOf'W* ] Lo« ^rojoadoi ,<- 1/ ,T. V ,/ r\ 1 \ / • ( [ ' r>W . •« \ \ r « ■’ X oenlo Roto a* .....'•...... 3 y /t»/i< fc’i /<«y V X • T) / ...... — - ...... > . . y de• ? So«k>rk L : i* * . v_ < y ! Wf/ouii» • V ^ \ i C LA^yMAflALA^yAWiA 0«>k A-5 '> ■{. (* j !*>* tJiiut X ,.vV' X. YU Nprvo \ y Lo lootedo > . \ - 1 X 7 7 7 A ^ * \ ^ ■ j ' ' \ <~ / ; • « / % ^ \ V Opodepe : * s > * .-’ X ' 0 C M»AU£XiTAOH| \timot* T % 3 310 0 0 0 ^ z 3 310 0 0 0 / n 1 a \ / x ! / x r>.' \ / ! A' A / / X - \ . z ! • A BL WlCANTU > , • ;> \ ■ • V' Akimedo ** A±> ' ' 7 / s>' % y z* * 'x ^/k < y x I :... #: y ^ Xv^yXx X • / y n/tZ x A n < 4 ' " \ s ' : • ' % ^k&Ld x .X \ / , M X x — . X. UAu.or. V- \ NV .; ' X V V: ■ F 'XX v-r v - ,* X iA ri A > y 7 ? z y X •C X; -. , Al ; €* Mezqmtif -» 26-2 .. \ Soo*o AAprjjQfrto v- f x V - , 3 A. / (7f- X -Z •■■ V x ' v 4 2 c ‘> ".-, -i ' -vn a : y f X > * v * — - ZL 'Y- Mgy - y : H\ / . V ' 4 ^ C^^TUJA A / i » i. I ^ > ' = & ' 7 7 7 7 1 J*xn ^ • ....«• ...... X : 'A / CAA$'"S. A ‘£1 Oorembvllo ^ "X% - - v c P ' s / X X 1 - i ,u.... ''•~i... e'i- • • • • • 4 • • V 1 ^ 7 fVN IX' A ', \ V' ■ v ;' 7 X 4 / u ^ooO 'T " ! - # \ 4 • / z (A .x$ \ V y I (J/M \ f * x Sue*. A** V s \ / /' - % \ v ''a 'Ma t A \ (' \ h \ q ■ / . < r h , _ 4 . / t x xS 7 E ^ ' - ' -" ^ / ; / . / f r J T r ~ ^ \ X , . . I T \ ii X / vV yt ..3zG s ^vyTX^_xi XAr; x # ••A V 7 t / —90C , • _ \- I . < y « i' y ! W/) / i / / / SogvOybotx • A yr x y- ? v V / y \ / Son RofoD*'^'' p i \ / -. ^ y x vj^.;,y x -A77X#? v • x. w- is -tA ‘ 1 T~^ "*T* "4 y y / t / m ^ X/ \ / A X> > \ • ’ 5- \ V : y 7 < \ / T. # x , „ . „ % ' % f xZ- X jX x;,7an%r&, yfiAV 1 , - y / K X ^ 7X )T!Z V ' 7 ' A./ . \ ,:/ ' - -v ' Y '" y \ x / / x i W - / .. : , : , ;(' / / Sookf^owiUn ^ j X ' ' • < ')' " , ^ 3 / 1 " . t v V ^ x ' . ' x / y . / , v ' / " y i ‘ \ ) • 0 »V' S'. y x>v 3UAT6S / y yj / V 71 X x y Z - -/• < << v » ' r a / » , ^ y :"'" y ^ V A S S a U ’fv x A ,\ - * v ' X ^ — y / 7 x N • 7* ■ |« HbeKfWle - 1_. <'3 y ' _ * > / ' X y 4 i?\, r , - y t / -s - "<>.• /' L f ... jf ^ _ V ’ ( CJX#«AUA 10» AAACH^A ■ > ■ b T ■y C f-AOHAlMA Lot /•nvu'f. A I Zv ‘v'y ^ , cz: < - «X*AA - A MAMACj*. Vv y f i o*^ Cowles ^ V 1 > * P*lm#fHo lo& Coneiot LA t*pOM.y4 r ..-i A ' ; A 3 f \ / r 4 . £ , Y i i 77 > 8 \ ; -- ^ ' r - " i x - . X X . lv-1 x _ ':. -_ - - ■ -^. x . __. EXPLANATION SC ALE Figure 10 1:50,000 PHOTOLINEAMENT MAP PHOTOGRAPHIC LINEAMENT 2 km OPODEPE MINING AREA FIELD MAPPED STRUCTURE SONORA, MEXICO 6?79/ ( 9 7 ^ 3 320 0 00 3 3 2 0 0 0 0 3 315 000 3 3 1 5 0 0 0 Son Jeronimo 3 310 OOP 3 3 1 0 0 0 0 I' Creston' ■ Lo Voriedod 3 305 OOP 3 3 0 5 0 0 0 ■ Lo Tina jo Socorro 3 300 OOP 3 3 0 0 0 0 0 3 295 OOP 3 2 9 5 0 0 0 EX PLANATION ------1 ROCK CHIP SURVEY LINE • STREAM SEDIMENT SAMPLE SCALE I 50,000 Figure 12 MINE GEOCHEMICAL SURVEYS ■ RANCH 2 km A HILLCREST OPODEPE MINING AREA SONORA, MEXICO ;SE RAMIREZ MUNOZ, MS THESIS. DEPT OF MIN. AND GEOL. ENG. J OF A. 19 79 i 525000 530000 535000 54000 0 545000 8 550000 3 320 000 3320000 1 1 1 i ! ! — ------.... . ■—— ------— • ------I ' 1 i i : | 1 — ------1 ------— — i • • " • • ! i ______1 ------I i * i ! • ! • • ; » ! ■ I i i ; ______| : i 1 1 ! i I •: . i • • ' • • • ! " • • ! 1 l 3 315000 ! ; ‘ : i * I ! 3315000 ! /zy/yyyyzz/ /////////////////////. V///////// V//////////////////A 7777777777,7 7 7 7 /7 /7 // 7 7 / 7 / 7 / / / / 7 7 7 7 /7 /7 $ ; ■ • # 1 # • I . i . . ' . • ; • ■ # » i • ! • r ^S an Jeronimo i 1 ______i I I ; : i | ! ' j • • e 1 # e # * * * # # • • ! i S : El Hue! ioo _____ i i i J !i , ' 1— i . ! i i ' ■ # . i . • • * * * i • ______i ' ; ; ! i: i F] 1 s------;, i i : ‘ i | . • • z # • • 1 • • # # • i A El Resbalader< i '1 | ; i ! ! i ! 1 i ! i : • i # * • • * j S 1 . ’ i # • • • : 1 i I ! 3 310 000 ______3310000 LL i i ! i ! • . • • • ' * ! • ! j i I 1 i . •1 : _1 M ■ ! ! i I ' ' 1 ■ • . i . # • • i • ■ ... ' ■ i - • i ' I 1j ■ ------,i— -- — i------i 1 L ! 1 : ! ! i - i ■ r * i • . : i ! • • 1 • i '1 1 !■ ! ! ■ | 1 : ! : : L 1 jI 1 !------1 1 j • • iI • • • • • ! i1 ! ■ | ! ; ■La Ctem ga AM El Creeton L i , ------® La Vartedad • • • . • • * i i ! 3 305 000 L 1 ■ i | ------r.—I ■ ■ 3305000 j # • • • • • | • • 1 j i ! L I- 1 j - La Tinaja ! • • 1 • e • # • 1 • # # ! ^ ? E I Soc >rro l J ! L 1 • 1 • # # # A ## * L. -XX xX tX W ' \\X\W\\\N ! 1 ' j # • # # # • ! * # • | 1 '//////////, ////////// Y////////A V////////Z //////////, '/////////A Y/////////Z v / / / / A m V///////// '////////// '////////// 1 • # • # # # 3 3 0 0 0 0 0 3 300000 I • • i t I 1i * 1 i . s ir 1 3 295 000 3 2 9500 0 o o o o O O o o o o O o o o o o O o m1 o EXPLANATION <% % O o % § m %*" m m m m w/y///// AREA A / XXWXXXN j- AREA B SCALE l; 50,000 Figure 13 • STREAM SEDIMENT SAMPLED CELL ii MINE ! LOCATION MAP OF THE SAMPLED CELLS km a RANCH r OPODEPE MINING AREA A HILLCREST SONORA, MEXICO JOSE RAMIREZ MUNOZ. US. THESIS. DEPT. OF mi. AND 6E0L. EUR. U OF A- 1979 £ ? ? ? / ' ^ 7 f > x .V-. •/ / '_ * «<' >At/ *.Srt •« . . /• t#K *• ■ \ f »' W ^ j r «*< vf> v*^’' ' s ■ v t •f. f ^ ***$ ■ » . ______;J ------— — 1 6 , 0 0 0 N ### * tv X ,VV , ki *4 F \ #• ' % " # X : # # , / ^v> "^1 • * . v . *; *v . - P ^ 4 I •* •« % * <■ # *. - »'> . A *y « 1 X 1 v Tk'i -t '' m E # ' ' ' ; ' ' V: - ' ' m : ? 3 £ llO -:- . ' - - f* ■ 4 , M f ■ £ " / fte p c e s o m f r,r k ^ . w m m . ^ e n R ^ t y M B H l , V V 4 i 4 K % '4 5 ^ ; \ > u vtV- & X: ’ f/ # \ & r n z y u < " * A ------— -fl1’ 1 ”■ ■ " 1 5 , 0 0 0 N • X r |iy* , • 9 d^/ " - .’ f ^ -.■ 4 r '+ s.+ r* r V ' ' V . r V - X * A '* X. i v i r / S: / \ . * i v » f x 'Av L ^ y '’’ • *1 / / ? * *>,7 t o Z • V X " f t X C o r bo A t r l ; - % \ S d k \ h Z 2 V • W» -T V % • V i . - B i ^ r X^«£S' 7 X X X X ; ■”c'^ "'X x ' < . ■ 14? i y vl % > '■«* > - / - ' 4 '.; :■ "' 1 4 , 0 0 0 N < A - : . ‘^^ M h , s : > U. /.V x / , . / *'%**. ‘*- X '• v > ; ‘ • IT B & a . M. V : y t % £ -#** A •Si m / K J r v V ^ 5 ■ X L- v X ' ,' . Vi ' f / h r ;Vv ^ y % X X ' v - ' X ' . ' - a * . 4 ■. r * :■ v ^ t - ' \ **' Z--. - ~*'.V \ », v ♦'' s * -X v. ’N * ' Y w ' y y X * # ' ^ „ . .; 'V t ,i<^ \ Z X x X ii.X :’ •> '';/• • '* VA ,. y x / ?% ^ ■ a # > v . ------L _ _ ------■»■"■■*■« 1 3 , 0 0 0 N — t— -.. ------T » ' f ; V f r ^ .r. » < » .* x > ^ ; Ao \ . • a. ] v. ^X j'V . 0»*< '; v ' v X 1 k X X > 4 i f V >- • >X v ? ^ '••/ >; ;2:'- ' •; . '•'r*>. vtx = " / . ’ V. 4iV s '. /- > «v •'•<• /C x . t’"1, : f^'lrf' 1 * . • L K «/ / t *5 4 >,j - % « • • j » , ™ 42* ^ X 4 % X ; * *■■ y Z r - \ 1 'tt’W* /- -> < jx V’ ' r "x * * *!• v: y * x ■ z g ’ / , * / A J V ' • < % V v e ‘ ;$'< ^ V .Vi ‘+‘fr irit •, j ‘*a * , « v ^ ' X . ' - f c - v •** r a # ! A 1 2 , 0 0 0 N ...... z , « t V ' 4 " ' . * • ■ * , • > , * % & A ^ * . -, ;• ,-f vf 1 Ik*' ♦* j ' ■*% = *%W: ##* ' r \ v .-.'tX v ;:> '4'" x l' f , ». # (. • v '-' : > i \ A : v ' : - . v x X X . , V > v y , \ ‘i -, <;• — ______z ______1 1 , 0 0 0 N •V . <, y \ , ^ f «H -J .' > V /,, V •'/V r, -' \ X a X : > v A ' *‘ * v i <*- > ^ A > ;' _ ? t ,:V; x^v' ^ " r< ^ . .-# . ». - fS?XAx-X;xXS * x - A m - 4 M 2 1 0 , 0 0 0 N ------% :>.w V ^.J, SI ,-S ## ' X ' ■ ### , »*••• Tv« 1 •• ,*t y , ' i x a V 5 . v > • ,<> ' ■ P B j •» W ;;v : l>3 J z z&m - m W j *? i - ;: ' " r '. , J “ v •• ) # • t - Y ^ W 4 " mm&m 9 , 0 0 0 N —-- - , - Z X - L ^ X - r — K I *sy^S ■ s f x x z . - . '.y '.X '.j.:;' aea i 1 •’S T ii.* « ^ i n r ■ O K a * B X / * y j . - a m \ 8,000 EXPLANATION > r f f e ALLUVIUM AND TALUS BRECCIA ------CONTACT , DASHED WHERE APPROXIMATE Quotemory — IN- SITU IRON OXIDE - CEMENTED MATERIAL * ~~ FAULT SHOWING DIP, DASHED WHERE INTERPRETED ~iy6 ATTITUDE OF BEDDING AND DIKES INTRUSIVE BRECCIA \ -v- ATTITUDE OF FOLIATION , 70 ACID TO INTERMEDIATE DIKE ROCKS < -w^- ATTITUDE OF JOINTS 7 , 0 0 0 N lOo RHYOLITIC Mk * JOINTS' IN SEVERAL DIRECTIONS, CLOSELY SPACED M 10b. ANDESITIC TO DIORiTIC 3 Tertiary (?) - (>*> B R E C C IA RHYOLITE PORPHYRY ^pp *£ SHAFT AND/OR ADIT t QUARTZ - K-FELDSPAR PORPHYRY A Ai------IA' C R O S S S E C T IO N L O C A T IO N QUARTZ MONZONITE PORPHYRY PI : © # 4 MONZONITE PHOTOGRAPHIC LINEAMENTS Z p, " m , - SONORAN GRANITE ^» » ••••••••• •** • AREA MAPPED BY 0 Comoduron, C. Hodgson, J. Hursh, SHEET 2 OF 2 # 1...... - W. L o d d e r, F L. L eon, D R e n d o n , J. T h o m o s ( 1 9 7 5 ) I 4 > Cambrian (?) “{] ~ Q U A R T Z I T E Li- r *, ^ zx> v*'f -%We4r . ' .*■ CRESTON GRANITE i w * ^ **>■*/'*' I ------,• > . - Paleozoic (?) Figure 3 ^ . 7 % " i M a n d /o r e o r h e r ( ? ) 6 , 0 0 0 N ------,■...... ------ANDESITE - DIORITE REGIONAL GEOLOGIC MAP AUGEN AND BANDED GNEISS OPODEPE MINING AREA 2 L t , SONORA, MEXICO SCALE 1:10,000 C alifornia _ . N US RK) LU|SCOLORADO AN ^ ( . _ ^ Pet Pefiesco OPuerto LO CATIO N MAP OF OPODEPE OPODEPE OF MAP N CATIO LO Tiburon Island OOA MEXICO SONORA, ol Kino ^ohlo RPI S LE A SC GRAPHIC 400 000 0 0 0 0 4 M I X c 0 U Y M S QEMPALME GUAY MAS hermosjllo OE REZ MUNi Z E IR M A R JOSE ucurp« OLo OLo o d a r o l o C 1 Mozocohd , 01 ID D VOBREGONCIUDAD onchl THESI S E H •T c Jovier Sc* o r a v l A __ Dam Obregdn C^Soyopo l Novillo El a T O MI d GE d , IN M OF PT. A Q t i A . P9I E T A Dom navojoa EG 9T I9 , A ENG. . i'*' i & S^7 > Y" :W^T. ______6 4 / i 6 , 0 0 0 N v - v r / k v#:; .t. ii 4k. /t r r*.' rf v ln; / •?’ A vj> * > f i |i '> &:#■ > M. t ri< t> #] K > . f » > 4kf > # V ### ; f? > W 14 v. mi#HRSA# ^ v • '■*** ■& lv w < . «5rP s « f > ■ Z'X K, C36m y; V W 4?' m w ■.J%* >*?- H|S ♦# '•3^ r W»a -fr * BB— ,^. K 4. ^ •’■>'•> ' ■+•**■*" 4 m s L . y . ■ ' k # > M g ^ 1 E F F m J*X *-*tFi m . ,vjr H r ■ V*5k ’ % ' " K - y X* * -v. ‘ V > ^ w m , ® >'(v ■v %WL t+Z-T ■ K | & X V : y ,-^Nrr *'fi «v A- vS," t+* "Y: jr F tl ‘W 2& ?WWb-4 , ^ iX^-X-ueS 't > < ^ i *9* 5 , 0 0 0 N \ fo Mr" • ^ 2 . «ir I C6>aao del % s v>; J S ff L X/ .» > •AW Hesbolodero x - " - x ec x v #4 \ X & X ■ • w x . ■ tt*- > f- V ,»• X AV * x \ 4 . 'V H. I > r % x A ■ X V f id f"- X . r . X' y Q P C t S f E \ Ha » , v- " s . « , . • - x - 4 *. \ M. j ^ a • ) . ■ V IfcLr % e •ii- j B r*f e f i k u g k — ■i . X . x r -X t y * \ X ,/ » » ,*• ™ r.* S s b -# XVV I!,000 N X* C . O C O N ■S* * * v * » 4 A*? f 4 - Z ; yk>t<' W F> ^vr-'V — % 9 , 0 0 0 N J*. t v 1 - •-■ — .! X - ' V L'X;; V W _■ ^ :'v ftii) , # 4 2 rS fc M A. r > ,k ■vc «t - * V r ' ~ ^ r ~ . A H4- ' 4^ o o o RX ;' B. v • .*!# %' < ^ ' SHEET / OF 2 / ■ SEE SHEET 2 FOR EXPLANATION OF GEOLOGIC UNITS. ' > m / ' m z A . . ♦' < L / ii \ \ fcfd \ i t * » v % . r* ih - * -a *: % ■ I K, SCALE Z . * z iM x: ^ I • 10 000 X. 8 3 ^ ^ V ; . , y ^ ^ \ - Figure 3 • J1,;. X > v 4 V I km • 78 REGIONAL GEOLOGIC MAP — ______6 ,0 0 0 N ,X OPODEPE MINING AREA SONORA, MEXICO 00 x l b b o o JOSE RAMIREZ MUNOZ. M.S. THESIS. DEPT OF MIN. AND/6EQL. ENG ) U. OF A 1979 ^ 7 . l?7e LOOKING N. 50° W. Section Section B-B' C-C' 1100 meters S II // II ^ 1000 IOOO n, \x // " ii * " '/ * n '' xX \\ II // ” „ xx ii ///// r •• :i 900 //, II ^ 11 / / xx //, // II «// » II // // II ■ f. 800 " \x \\ / / / / / ' ii // =■ xX // H II \\yy \\« V VX, ' - \x // ^ ^//. 11 \\ II ^ II ^ II v // x\ // II II „ f // II II mm® 700 / v / x / - ^ W II // H a s II / / H * A \\ * II 600 / " II n II V. H II // ii n II * ii ^ ii X\ * II // = / / x x/, y * // II * II II \\ ^ 500 // - II II "// 1 // _ V = vl II < Z II „ ^ zz V xx = IU X-\x/^,-\-2 I \/ ss ^ H <5- \\ » _\\ * V \ I ~ s / \ II H * XX // „ // I' H 400 /////. w * * // II 300 EXPLANATION Q uaternary - £ f J°0 13 ALLUVIUM AND TALUS BRECCIA ------CONTACT, DASHED WHERE APPROXIMATE ------FAULT Tertiary (? ) - RHYOLITE PORPHYRY "_'s S " - SONORAN GRANITE Figure 7 SCALE GEOLOGIC CROSS SECTION A-A' Cambrian (? ) “L QUARTZITE, SHOWING BEDDING HORIZONTAL VERTICAL OPODEPE MINING AREA I 10000 hSOOO M N - 0 -1 J V CRESTON GRANITE Paleozoic (?) SONORA, MEXICO a n d /o r earlier (?) / / 2 / / ANDESITE - DIORITE 1 AUGEN AND BANDED GNEISS JOSE RAM IRF7 MuROZ. M.S. THESIS. DEPT OF MIN. AND 6E0L. ENG. U. OF A.. 1979 ^ 5 ^