summary of structure and mineralization...
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SUMMARY OF STRUCTURE AND MINERALIZATION AT
LA VARIEDAD, LA BELLOTA AND LAS AMARILLAS PROSPECTS:
LEON PROPERTY, CENTRAL SONORA, MEXICO
By: Dr. Jonathan A. Nourse, Professor Department of Geological Sciences California State Polytechnic University Pomona, CA 91768 Mr. Paul Stubbe 4522 County Road 203 Durango, CO 81301
Submitted To: Mr. Lance Geselbracht, President and CEO Dr. James J. Irwin, Exploration Manager Colibri Resource Corporation Nanaimo, British Columbia Date: January 17, 2008
TABLE OF CONTENTS
INTRODUCTION p. 1
LA VARIEDAD COPPER MOLYBDENUM ANOMALIES p. 1
LA BELLOTA GOLD PROSPECTS p. 4
LAS AMARILLAS POLYMETALLIC ZONE p. 6
CONCLUSIONS AND RECOMMENDATIONS p. 7
CERTIFICATE OF QUALIFICATIONS p. 9
ILLUSTRATIONS (appended after page 10) Figure 1. Structural map of La Variedad area showing mineralized quartz veins, molybdenum assays from rock chip samples, and proposed diamond drill holes Figure 2. Structural map of La Variedad overlain on molybdenum in soil anomaly map Figure 3. Structural map of La Variedad overlain on copper in soil anomaly map Figure 4. Stereonet plot showing quartz vein orientations NE of La Variedad Figure 5. Stereonet plot showing quartz vein orientations SE of La Variedad Figure 6. Geologic and structural map of La Bellota prospects showing assays of surface samples in g/ton Au Figure 7. Photograph of primitive mill (arrastra) probably dating from Spanish colonial times. Large stone adjacent to hammer was attached to a chain and used as grinding stone, probably powered by a mule. Figure 8. Photograph of recent (circa 1980s?) mine working along northernmost high-grade gold vein at La Bellota. View is to S70W. Figures 9. Side view of the arrastra shown in Figure 7. Note the two grinding stones. Figure 10. One of the other ten pre-1850’s arrastras preserved to varying degrees at La Bellota. Figure 11. Structural map showing location of all drill holes completed at Las Amarillas as of December 15, 2007. Colored dots indicate values of copper in soil, in ppm. Map is modified somewhat from illustration created by Roberto Rivera.
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INTRODUCTION This report summarizes salient results of our January 3-5, 2008 field investigation of
three sites on the Leon Property of central Sonora. Primary objectives were: (a) to
better understand the structural setting of mineralization at La Variedad, La Bellota, and
Las Amarillas sites, (b) to spot several locations for prospective diamond drilling on the
La Variedad copper-molybdenum soil anomaly, and (c) to collect rock-chip samples
from key outcrops. Below we describe the basis for our choice of five drill holes that
should intersect three separate copper-molybdenum anomalies centered about steeply
SSW dipping quartz veins and stockwork in altered granodiorite. Our investigation of La
Bellota revealed at least three steeply dipping, WSW-striking high-grade vein systems
that have yielded significant gold assays from surface samples (six samples so far have
run between 4.1 and 17.6 g/ton Au; four others are on the order of 1 g/ton). All three
vein systems are exposed by old mine workings; one coincides with a collapsed trench
probably dating back to Spanish colonial times. Our mapping at Las Amarillas
demonstrates a major NNW striking normal fault that disrupts a system of three or four
ENE-striking mineralized quartz veins that converge in the vicinity of San Antonio mine.
Recent diamond core drilling has intersected narrow zones of anomalous copper-zinc-
silver-gold mineralization that probably coincide with individual veins.
LA VARIEDAD COPPER MOLYBDENUM ANOMALIES Several prospective drill targets are situated in low ridges the vicinity of La Variedad
(Figure 1) that coincide with spectacular soil anomalies exceeding 200 ppm
molybdenum and 1000 ppm copper (Figures 2-3). Our investigation focused on three
east-trending ridges containing especially abundant quartz veins strongly mineralized
with hematite, molybdenite, copper sulfides, and various copper oxides (see
descriptions below). These veins display a very strong preferred orientation (structural
trend) of N55-85W/55-85SW, as demonstrated by Steronet plots of outcrop
measurements (Figures 4-5). The host rock is Cretaceous medium-grained,
equigranular granodiorite intruded by occasional 6cm to 3m wide dikes of fine-grained
felsite or aplite.
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Forty rock chip samples from mineralized quartz veins near the three target zones
(Figure 1) yield analyses averaging 658 ppm molybdenum (range is 50 ppm to 3660
ppm Mo; the average excludes two high-grade samples containing 14,910 ppm and
26,740 ppm Mo). Nine samples of mineralized and variably stockworked granodiorite or
felsite situated between prominent outcropping veins have also yielded anomalous
molybdenum and copper values (272 ppm Mo average; 112 ppm Cu average). During
this current study, we collected three additional rock chip samples to test our inference
from the soil anomalies that altered rock between major quartz veins contains significant
copper and molybdenum. These samples average 428 ppm Mo and 125 ppm Cu.
Prospective drill holes VDH-1, VDH-2, and VDH-3 were spotted within a +200 ppm
molybdenum in soil anomaly located directly northeast of La Variedad camp (Figure 2).
Several small anomalies of +500 ppm copper in soil occur in this same area (Figure 3).
We also walked the ground directly west of VDH-3 to ascertain a geologic explanation
for the prominent north-trending +1000 ppm copper in soil anomaly. Here we were not
impressed with the density of veins and stockworking, nor the degree of alteration in the
granodiorite. Furthermore, rock chip samples previously collected from this copper
anomaly and its continuation to the northeast yielded assays ranging from 25 ppm Cu to
407 ppm Cu, significantly less than the soil values. We speculate that some kind of
weathering process has mobilized the copper and precipitated it in soils at higher
concentrations than in nearby bedrock. Further rock chip sampling is recommended to
test the significance of this copper in soil anomaly.
VDH-1: UTM 528077E, 3305904N, Azimuth = N10E, Inclination = -45° This hole
should intercept a zone of quartz-molybdenite stockwork veins oriented N70W to E-W
and dipping steeply to the south. A secondary set of ENE striking veins intersects the
primary veins along this ridge (Figure 1). Most veins occur as centimeter to half meter
wide quartz with disseminated molybdenite crosscutting a moderately altered biotite
granodiorite host rock. The drill hole is designed to test a +200 ppm molybdenum in soil
anomaly at this site, as well as a nearby +500 ppm copper in soil anomaly.
VDH-2: UTM 527963E, 3305910N, Azimuth = N10E, Inclination = -45° This hole is
designed to test the same molybdenum and copper soil anomalies and same vein set
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as VDH-1. It is located approximately 115 m west of VDH-1 to test continuity of
mineralization along strike.
VDH-3: UTM 527818E, 3305851N, Azimuth = Due North, Inclination = -45° This
hole should intercept a set of nearly E-W trending, steeply south dipping quartz-
molybdenite veins. On the surface just north of the drill site, the veins and float contain
disseminated bornite and minor malachite staining. The hole will test a +200 ppm
molybdenum in soil anomaly. It also coincides with the east edge of a +1000 ppm
copper in soil anomaly.
Prospective drill hole VDH-5 was spotted at the south edge of a separate combined
copper-molybdenum soil anomaly about 750 m northeast of La Variedad camp.
VDH-5: UTM 528210E, 3306327N, Azimuth = Due North, Inclination = -45° This
hole should intercept a set of E-W trending, steeply south dipping quartz-molybdenite
veins. The veins can be up to one meter thick and display good dense stockwork in
places. Much of the surrounding granodiorite is bleached with argillic alteration. Acid
leached boxwork texture is observed in this target area with strong limonite after pyrite
and locally good jarosite developed in gossanous quartz samples. Some vein breccia
can be seen nearby. Three rock chip samples collected from vein systems that strike
WNW into the target zone have run 600ppm, 850 ppm, and 1200 ppm Mo, respectively
(Figure 1). The hole will also test a coincident copper-moly soil anomaly with values
exceeding 200 ppm Mo and 1000 ppm Cu at this location.
Prospective drill hole VDH-4 targets a network of SW-dipping quartz veins and aplite
dikes situated southeast of La Variedad camp. Compared with the previous two target
areas, veins in this area are less steeply dipping and strike somewhat more northerly
(average orientation is N55W/74 SW; see Figure 5).
VDH-4: UTM 528232E, 3305456N, Azimuth = N30E, Inclination = -45° This hole
should intercept a set of N50-70W trending, 65° SW dipping quartz veins with
disseminated molybdenite. The alteration in the host granodiorite and the vein density is
not as great here as at VDH 1 and VDH-2, but there appears to be some good
stockwork associated with a felsite dike that crosscuts the granodiorite parallel to the
veins. The hole targets a coincident molybdenum-copper in soil anomaly at this location
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on an old road near the ridgetop. Directly along strike to the northwest, two rock chip
samples from the same vein system have run 730 ppm and 1040 ppm Mo, respectively.
A good alternative to drill hole VDH-4 is the prominent northwest-trending vein
system that crosses the main dirt road about 150 m south of VDH-4. We have mapped
outcrops of this vein system semi-continuously ~1000 m to the northwest, where it
intersects the road leading to La Variedad. Eight rock chip samples from this vein
system yielded assays averaging 664 ppm Mo and 183 ppm Cu. The southeast end of
the vein system coincides with a +1000 pm copper in soil anomaly (Figure 3).
Therefore, this southwest-dipping vein may present a decent drill target (with the hole
angled toward the N30E). However, as discussed earlier, we note that the values of
copper in soil exceed those taken from outcrop, suggesting again that some unknown
process has concentrated copper in the soil at expense of the local bedrock.
LA BELLOTA GOLD PROSPECTS
The potential significance of La Bellota was pointed out to one of us (Stubbe) by
Pedro Lopez, a resident of Carbo who works as a field assistant for Coilbri Resource
Corporation. Ten rock chip samples collected last April by Paul Stubbe and Jim Irwin
from this area of old mine workings have returned values ranging between 0.4 to 17.6
g/ton Au. Three subparallel, WSW striking, steeply dipping veins have been worked in
a small way (Figure 6). The presence of more than 10 arrastras (primitive mills)
adjacent to the principle arroyo testify to the serious effort given to one of these mines
by early Spanish(?) colonists, probably prior to 1850. Two more recent mines, probably
excavated during the 1980s, follow high-grade veins of similar orientation to the
presumed Spanish workings (Figures 7-10).
The ancient mine workings are located directly across the main arroyo and
approximately 100 m south of the arrastras. Here a timbered stope intersects what
appears to be an old trench but is likely a collapsed area above underground work on a
vein. Angled trench walls suggest that the mined vein had an orientation of S45 to
60W/65NW. Three dump samples of quartz-pyrite-arsenopyrite-galena material
collected along a 200 m length of assayed 4.8 g/ton, 5.9 g/ton, and 9.3 g/ton Au. This
vein is thought to be the source of material for the early arrastras. The vein is hosted by
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aphanitic rhyolite that is well-silicified and strongly bleached and argillized in places.
Given its location adjacent to the main arroyo, we suspect that the original Spanish
mine extended only to the water table, inferred to be ~20 m here. Sophisticated pumps
were likely unavailable at that time.
The principal La Bellota mine is situated up the steep slope approximately 300 m
south of the ancient workings (Figure 6). This mine consists of two adits that are
probably connected: one at the end of a recent dozer road and another on the same
vein but higher up the slope and covered by vegetation. The vein is oriented
approximately S70 to 80W/80NW. The entrance to the lower adit is characterized by an
intensely argillized rhyolite, several meters thick, with 2 to 8 mm rhythmic bands of
quartz-limonite veinlets. Our sample from this unit taken 4 m below the adit assayed
0.38 g/ton Au. A 2 m channel sample at the mouth of the lower adit assayed 15.2 g/ton
Au. Another sample of the clay altered material returned 0.98 g/ton Au. The adit
appears to be driven on a zone of strong silicification with abundant sulfide
mineralization. Pyrite, arsenopyrite and some galena are present. The upper adit has a
dump at the mouth consisting of red-orange-black limonitic gossan material. The host
rock here is a silicic granular rhyolite or rhyolite breccia with fine disseminated sulfides,
probably pyrite.
Across the main arroyo and to the northwest of the arrastras is another old vein mine
(circa 1980’s?). This open cut, oriented S70W/70SE, is about 15 m deep and 1-2 m
wide. It has a small dump of sulfidic material that assayed 8.6 g/ton Au in the one
sample taken. Related trenches extend about 60 m to the southwest. This quartz-
pyrite-galena vein is hosted by argillized granite near a presumed intrusive contact with
Upper Precambrian(?) quartzose conglomerate and sandstone. The granite terrain
around this old mine is traversed by several other quartz veins with similar orientations.
One of these veins, located 150 m northeast approximately along strike from the mine,
assayed 17.6 g/ton Au. About 150 m farther west, a gossany quartz vein marks the
contact between aplite and phyllitic argillite. Our sample from this vein returned 1.4
g/ton Au.
It is interesting that veins south of the principle arroyo dip steeply northwest while
those on the north side dip southeast. This suggests that some kind of intersection or
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convergence may occur at depth or in the center of the valley. Also very interesting is
the fact that none of these veins have been drilled, nor have the workings been
extended along strike into areas of hydrothermally altered and potentially mineralized
outcrop. Given the straightforward geometry of this system, the occurrence of high
grade samples from all three veins, the probability that two of these veins have only
been mined to depths of <20 m, and the current high price of gold, the La Bellota area
begs for a serious exploration endeavor. We strongly recommend: (1) soil sampling of
the area along a tight grid, (2) detailed rock chip sampling of veins and altered wall rock
exposed within the gridded area, and (3) detailed geological mapping of the veins, their
leucocratic granite and volcanic host rocks, and associated alteration zones.
LAS AMARILLAS POLYMETALLIC ZONE The Las Amarillas zone consists of three prominent ENE striking, steeply NW
dipping quartz veins that converge in the vicinity of San Antonio mine, an internal claim
not held by Colibri (Figure 11). Chip samples collected from the substantial
underground mine workings at San Antonio and from surface expressions of the same
veins have yielded assays between 1.2 and 1.9 g/ton Au and between 250 and 600
ppm Ag, along with anomalous copper, zinc, and lead. In the immediate area of San
Antonio Mine, the host rock is medium grained, equigranular Cretaceous granodiorite
containing common dikes and small irregular intrusions of aplite or felsite. Across the
arroyo to the northeast, the vein system diverges somewhat, and may bifurcate unto
four separate veins. These veins were the principle target of recent percussion and
diamond drilling (see Figure 11), based on the presence of a modest mine working
whose dump has yielded promising metal assays of 5.18 g/ton Au and 288 g/ton Ag
(see Colibri Corporation prospectus).
Southwest of San Antonio mine, the three veins appear to continue through a
prominent hill, but their surface outcrops are thinner. The host rock in this area is also
different: weakly foliated, medium grained porphyritic biotite granite that resembles a
Precambrian unit mapped by one of us (Nourse) in vicinity of La Tinaja. Our mapping
indicates that a significant normal fault separates the veins at the main San Antonio
Mine workings from the southwestern Precambrian body. This fault, oriented N to
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N30W/42SW, is well-exposed at the mouth of the southwesternmost adit where Ridel
shears indicate normal displacement. Fault striations rake 75 to the southeast.
Displacement on this normal fault has caused deeper levels of the vein system to be
uplifted at San Antonio mine relative to shallower levels that cut the Precambrian hill.
So far (as of December 31, 2007), assays have been received from diamond drill
holes LEDH-1, LEDH-2, and LEDH-3, which were directed SSE across the strike of the
main veins across the arroyo from San Antonio mine. Results indicate several narrow
intervals containing anomalous gold, silver, and base metals that probably correspond
to intersections of the mineralized veins. The richest intercept was a 1 meter interval
near the top of LEDH-2 that ran 1.2g/ton gold, 134 ppm silver, 2.05 % copper, 0.9 %
lead, and 0.75 % zinc (see details in January, 2008 news release). Assays have yet to
be received from DH-4 and DH-5 (this last drill hole was directed SSW across the veins
in the Precambrian body).
CONCLUSIONS AND RECOMMENDATIONS We have spotted locations for five diamond drill holes near La Variedad that target
several +200 ppm molybdenum in soil anomalies that coincide with rock-chip samples
averaging 658 ppm Mo (Figure 1). These prospective drill holes should intersect three
separate zones containing Mo-mineralized quartz veins with consistent orientations of
N85W to N60W/60 to 85SW, separated by moderately altered and stockworked
granodiorite. Drill roads have yet to be constructed, but the relatively gentle topography
should make it easy for a bulldozer to accomplish this. Sites for proposed drill pads are
prominently flagged. We recommend that drilling commence as soon as possible while
the weather conditions are still good. Drill hole lengths of 150 m to 200 m should be
sufficient for a preliminary test of these targets.
It would be worthwhile to use the air percussion drill to test the highest grade
portions (+1000 ppm) of the copper in soil anomaly. We are somewhat puzzled by the
existence of these high copper values in soils from areas where all adjacent rock chip
samples assay between 25 ppm Cu and 500 ppm Cu. It is important to determine
whether the high-grade soils represent a thin near-surface effect of concentrating
copper by weathering, or a more substantial supergene enrichment at depth.
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We are especially impressed by La Bellota’s potential to be a lucrative gold
prospect. The presence of numerous primitive Spanish(?) arrastras suggests that early
miners had good success in recovering high-grade ore from the vein along the arroyo.
The fact that five of the samples collected at the surface have yielded gold assays
exceeding anything yet sampled or drilled at Las Amarillas demands immediate
followup study. It appears that two of the three high-grade veins in this area have been
previously mined only to water table depths of ~20 m. At the very least, La Bellota
deserves a detailed soil and rock chip sampling program, coincident with geological
mapping, and perhaps air-track drilling. Completion of this preliminary exploration
should guide decisions about where and if to drill diamond core on the site.
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CERTIFICATE OF QUALIFICATIONS
I, Jonathan A. Nourse, certify the following: 1) I am a consulting geologist residing in La Verne, California. 2) I am employed at California State Polytechnic University, Pomona as a full Professor in the Geological Sciences Department. 3) I obtained a Bachelors of Science degree in Geological Engineering from Colorado School of Mines in 1983. 4) I obtained a Master of Science degree and PhD in Geology from the California Institute of Technology (Caltech) in 1985 and 1989, respectively. 5) I have conducted geological field studies focused on the tectonics, structure, and mineral deposits of Sonora, Mexico since 1985. 6) I personally conducted mapping of geology and structures, and collected rock chip samples on the Leon mineral concession over a period of seven weeks between September, 2006 and January, 2008. 7) I serve on the Colibri Resource Corporation board of directors. I hold stock options in the company as specified in public documents posted on www.Sedar.com. 8) This report represents my unbiased professional assessment of the geology, structure, and mineralization on the Leon mineral concession, based on compilation of the limited data acquired to date. 9) Permission is granted to use this report in a company prospectus or other financial offering. Jonathan A. Nourse, PhD. January 17, 2008
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CERTIFICATE OF QUALIFICATIONS (continued)
I, Paul Stubbe, certify the following:
1) I am a consulting geologist residing in Durango, Colorado. 2) I obtained a Bachelors of Science degree in Geological Engineering from Colorado School of Mines in 1983. 3) I have conducted mineral resource investigations and supervised drill projects the western United States, Peru, Guyana, Burma, Philippines, Kazakstan, Kyrgyztan, Australia, northern Canada, and Mexico since 1983. 4) I personally conducted mapping and rock chip sampling on the Leon mineral concession over a period of four weeks between April, 2007 and January, 2008. 5) This report represents my unbiased professional assessment of the geology, structure, and mineralization on the Leon mineral concession, based on compilation of the limited data acquired to date. 6) I have no financial interest in Colibri Resource Corporation. 7) Permission is granted to use this report in a company prospectus or other financial offering. Paul Stubbe, BSc. January 17, 2008
Figure 1. Structural map of La Variedad area showing mineralized quartz veins, assays of rock chip samples in ppm Mo, and proposed drill holes.
Figure 2. Structural map of La Variedad overlain on molybdenum in soil anomaly map
Figure 3. Structural map of La Variedad overlain on copper in soil anomaly map
Figure 4. Stereonet plot showing quartz vein orientations NE of La Variedad
Figure 5. Stereonet plot showing quartz vein orientations SE of La Variedad
Figure 6. Geologic and structural map of La Bellota prospects showing assays of surface samples in grams/ton Au
Figure 7. Photograph of primitive mill (arrastra) at La Bellota, probably dating from Spanish colonial times. Large stone next to hammer was attached to a chain and used as grinding stone, probably powered by a mule.
Figure 8. Photograph of recent (circa 1980s?) mine working along northernmost high-grade gold vein at La Bellota. View is to S70W.
Figure 9. Side view of the arrastra shown in Figure 7. Note the two grinding stones.
Figure 10. One of the other ten pre-1850’s arrastras preserved to varying degrees at La Bellota.
Figure 11. Structural map showing location of all air-percussion and diamond drill holes completed at Las Amarillas as of December 15, 2007. Colored dots indicate values of copper in soil, in ppm. Map is modified somewhat from illustration created by Roberto Rivera.