14

Laboratory Hand Sorting

Separate 1000-pound portions of each of the two samples were crushed to
minus-3-inch size and then screened into plus-1-1/2- , plus-3/4- , plus-1/4- ,
and minus-1/4-inch fractions. Each of the plus-1/4-inch fractions was care-
fully hand sorted for beryl. The results of assaying the products are
presented in table 1.

TABLE 1. - Results of laboratory hand sorting

Sample No. 7 Sample No. 8
Analysis,|Distribution, Analysis, |Distribution,
Product Weight,} percent percent Weight, |] percent percent
percent BeO BeO percent BeO BeO
Sorted beryl.. 0.15) 4.71 10.5 0.03 1.90 2.4
Sorted rejects} 56.35} 0.036 29.8 62.10] 0.021 57.8
Primary
minus-1/4-in. |__43.50 +09 59.7 37.87 024 39.8
Calculated
heads... 100.00 0.067 100.0 100.00] 0.022 100.0

The data given in table 1 show that only 10.5 percent of the beryl in
sample No, 7 and 2.4 percent of the beryl in sample No, 8 were recovered in
hand-sorted concentrates assaying 4.71 percent BeO and 1,90 percent BeO,
respectively, The unexpected low recovery of beryl obtained by sorting
remains unexplained; after the sorted rejects were recrushed, microscopic
examination revealed that no significant amount of beryl was overlooked
during sorting,

The pegmatite in both samples was unusually friable; crushing to minus-
3-inch size reduced approximately 40 percent of the weight of each sample to
minus-1/4-inch, The minus-1/4-inch fractions contained 59.7 percent of the
beryl in sample No, 7 and 39.8 percent of the beryl in sample No, 8. These
facts indicate that a major portion of the beryllium occurs either as unde-
tected minute crystals of beryl or as a constituent of one or more of the
other minerals,

Stage Crushing and Screening

The sorted-reject products, crushed to minus-1/4-inch size, were combined
with the primary minus-1/4-inch fraction, After dry screening to remove a
clean mica product of plus-3-mesh size, the undersize was successively reduced
to 6- , 10- , and 14-mesh fractions by stage crushing in rolls, Additional
mica was recovered by screening the crushed ore prior to each reduction to the
next finer size, By these means, approximately 70 percent of the mica was
recovered in concentrates estimated to contain 90 percent mica.

Flotation
Satisfactory mica concentrates from both samples were obtained by flota-

tion, but flotation of beryl from the two ores proved difficult, From the
higher grade sample (No, 7, containing 0.065 percent BeO), only 45 percent of


less than 1 inch in diameter. Muscovite is a common accessory mineral and
occurs in flakes and books from microscopic size to 2-1/2 inches long.
Locally, the wall zone contains as much as 10 percent muscovite. Garnet and
black tourmaline are minor accessory minerals in this zone.

Beryl occurs as irregularly disseminated euhedral to anhedral blue-green
crystals. The beryl crystals are as much as 2 inches in length, but the aver-
age size is about one-quarter inch. A 300-pound surface sample of the wall
zone assayed 0.6 percent beryl.

2. Oyter intermediate zone: This zone extends about 130 feet along the
hanging-wall side of the deposit. It ranges from less than an inch to a maxi-
mum of 25 feet in width, but probably averages about 7 feet. It is made up of
55 percent perthite and 45 percent quartz. The grains average between 4 and
12 inches in diameter; some are as much as 3 feet in diameter.

Although no beryl was observed in either the drill core or in opencuts,
assays of the drill core showed small amounts of BeO.

3. Inner intermediate zone: The inner intermediate zone pinches and
swells, and ranges from 2 to 12 feet in width. It consists of 50 percent
plagioclase and orthoclase, 40 percent quartz, 7 percent muscovite, and 3 per-
cent beryl and other accessory minerals including tourmaline, microcline, and
garnet. The feldspar has a medium texture and a somewhat platy habit.

The beryl occurs typically in clusters of both large and small crystals.
The beryl crystals range from 1 inch to 1 foot in diameter, and some are as
much as 5 feet in length. A few small grains are scattered in the rock
between clusters. Both euhedral and anhedral beryl are common. In the sur-
face workings, the beryl recovered by sorting constituted about 2.3 percent
of the material handled.

The zone also yielded scrap mica from surface shoots and streaks of fine-
to very coarse-grained muscovite. The streaks are from 1 inch to 5 feet wide
and from 1 to 30 feet long. The largest books are as much as 15 inches long
and 6 inches thick, but no sheet mica has been obtained from them because the
books are heavily ruled and wedged and have "A" structure and many mineral
inclusions. The fine-grained mica consists of flakes and books that are
oriented at random, range from microscopic to 3 inches in diameter, and are
intimately intergrown with quartz, feldspar, tourmaline, and beryl.

4. Core zone: The core zone measures a maximum of 240 feet in length,
35 feet in width, and 150 feet down the plane of the dip. The core consists
of about 96 percent perthite, 3 percent quartz, and 1 percent plagioclase,
muscovite, tourmaline, and garnet. Some of the grains of perthite attain
lengths of as much as 10 feet. Quartz occurs in coarse masses as much as 4
feet in dimension.

Beryl has been found along the margins of the core, but has not been
observed in the interior.


18

APPENDIX III

REPORT OF SPECTROGRAPHIC ANALYSIS, DIAMOND-DRILL-CORE SAMPLES

Elements
Sample No. Ag [Al |As |Au|B|Ba |Be |Bi|Ca|/Cd|Ce |Co [Cr |Cs |Cu|Fe|Ga|Ge|HE
s -| Al -| -]-] D] D] -] By -| -] -] EJ] Dj] Ej By E]} -] -
s -| Aj] -| -/E] E] D}] E} By -| -] -| Fj] Dj E] B] EY] -] -
s -| A] -| -|]D] E] D] -| D] -] -] -] E] D] E}] BY] E] -} -
s -| Aj] -| -JE] E] D} -]| By -| -| -| Fj E] E] B] E] -] -
s -| A] -| -JE] E] D} -| By -| -| -| F] Dj] E] B] E] -] -
s -| Al -| -JE] D] D] -| B/ -| -] -] Fj] Dj Ej By E] -| -
s -| Al] -| -JE] D] D] -| B] -| -] -|] F] Ej] E] By E] -]| -
s -| A] -| -JE] DJ] E}] D} B/ -| -| -| F] Dj] E] By] E] -| -
s -| Al] -| -/E] E] E}] -| Bi] -| -| -| F] EJ] E] B] E] -] -
s -| Al] -| -JE] E| D] -} Bi -| -| -| F| E| Ej BI Ej -| -
Elements
Hg |In |Ir |K |La| Li |Mg |Mn |Mo|Na [Nb |Ni |Os |P |Pb|Pd|Pt |Rb |Re
S Divcccccccvccscees -| -| -|B] -| C] Cj} Cc] -| B) E] -] -j-] E} -}] -] D -
s 10.. wees -| -] -IB] -| DJ] Cc] C} -] By] -] -] -J|-] E] -| -| D -
s . -| -| -|B] -| D] Cc] Cc} -| By -] -] -J-] E] -] -| D -
s 12.. oe -| -| -|B] -]| DJ] Cc] Cc] -| By] -| -| -|-] E] -]| -| E -
S 13 .sccceeeee -| -| -|B] -| C] C}] Cc} -| By) -] -| -J-] E] -] -] D -
s -| -| -|B] -] DJ] C] C}] -| By] -| -| -J-] E] -] -]| D -
Ss -| -| -|]B] -] Dy] C}] Cc] -| By -] -] -J]-] E] -| -] D -
s -] -| -JA] -]| C] Cc] DI] -| By -] -] -J-] E] -| -| D -
s -| -| -|B] -| DJ] C}] D}] -} By] -| -| -J-] E] -] -] D -
s -|-| -1B] -| DI] C| D] -| B) -| -| -|-| Ej -| -| E -
Elements
Rh jRu |Sb |Sc [Si |Sn|Sr |Ta|Te |Th|Ti/T1 | U| V Yj Zn [Zr
-[ -[-] -] Al -] DU) -] -] -| Dl) -]-]-]-]- - | D
-} rp arp] Ale] DD) -} -} =] DP ep eye ded- -|E
em} -t-] -] A} -] D] -} -] -] Dl) -]}e-ye-ded- -|E
-[-p-} -] Al -] DU) -} -[ -]| BE] -]-]-de]- -|E
-| <p -} -] Al -] D] -] -] -] DJ) -}-]eded- -|E
-}-}-] -] Al -] C] -] -] -] DP -}-]-dey- - E
-] ee} -} -] AJ -] C] -] -] -]) DE -] ep -d-d- -|E
wtede A} -| C] -] -]} -]| Di -Jert-f-]- - E
“| -] -] -] A] -] El] -] -] -]| D) -]}-]-d-]- - E
-| -[ -] -| Al -| Di -| -| -| DI -|-|-J-1- - JE

MMU OWP 1 INHANHNAHNHAHNHNH

Not detected.

Probably
Probably
Probably
Probably
Probably
Probably

>10 percent.

1 - 10 percent.

0.1 - 1 percent.

0.01 - 0.1 percent.
0.001 - 0.01 percent.
0.0001 - 0.001 percent.

INT.<8U.OF MINES, PGH. PAL

1837


CONTENTS

Introduction and summary...
Acknowledgments..
Location and accessibility
Physical features and climate..
History, ownership, and production.
Description of the deposit.
Work by Bureau of Mines.
Preparatory work.....
The adit.ccccscscscccccscscseces
Sampling on adit level...
Diamond drilling. ....csccecveeee
Sorting plant........
Metallurgical tests..
Laboratory hand sorting....
Stage crushing and screening
Flotation. .sssccsssscssccaes
Marketing of beryl, mica, and feldspar.....
Appendix I. - Summary of diamond-drill-hole data..........
Appendix IL. - Diamond drilling, footage, and percent
LECOVELY sees cesesececocccecseeeseeseesseeereeessesseeees
Appendix IIL. - Report of spectrographic analysis,
diamond-drill-core samples........ eevee eee eneere scence

ILLUSTRATIONS

Location map, Hyatt Ranch pegmatite, Larimer County,
COLO. ecessecccccccecesecccvcsccceserseessesressceees
2. Topographic map, showing surface geology and mine
workings, Hyatt Ranch pegmatite..c.cccccccccecceeces
3. Longitudinal section through adit, showing zoning and
sample locations, Hyatt Ranch pegmatite....
4. View of adit portal and adjacent area......
5. Sorting plant..cccccccccccccccccccscvcccvcvcssecvceees

TABLE

1. Results of laboratory hand sorting....eccsceeces

to
cy
ecooussnnef

10
12


15

the beryl was recovered in a cleaned concentrate that assayed 4.5 percent BeO.
Sample No. 8 (containing 0.022 percent BeO) proved even more difficult to con-
centrate; only 35 percent of the beryl was recovered in a concentrate assaying
0.65 percent BeO.

Chemical and microscopic studies of flotation, middling, and tailing prod-
ucts indicated that the low recovery of beryl resulted mainly from loss in the
large amount of untreatable slime formed by grinding the ore to flotation size.
The low grade of the beryl concentrate is attributed to the difficulty in
effectively separating the beryl from the tourmaline and apatite that tend to
float with the beryl. The very low grade of the two ore samples also contrib-
uted to the difficulty in obtaining high-grade beryl concentrates with high
recovery.

MARKETING OF BERYL, MICA, AND FELDSPAR

The principal purchaser of beryl in the Rocky Mountain region is (in
October 1959) the Government depot at Custer, S. Dak. To be acceptable, the
product must be in the form of clean beryl crystals cobbed free of waste and
must have a BeO content of not less than 8 percent. Beryl purchases under
the Government buying program are based on a short-ton unit (1 percent, or 20
pounds) of contained BeO. The price generally ranges from $40 to $50 per unit.

A limited market for beryl produced in the region is provided by the
Beryl Ores Co. of Arvada, Colo. The price for beryl sold to this company is
based on the price of imported material and, consequently, is variable.

According to information received from mine operators in the region, the
average 1958 price for scrap mica was $25 per short ton f.o.b. Pueblo, Colo.;
and for either potassium feldspar or a mixture of potassium and plagioclase
feldspars, the 1958 price was $6.13 per long ton f.o.b. Denver, Colo. How-
ever, in the last half of 1958, the Pueblo and Denver mills stopped purchasing
scrap mica and crude feldspar, and at present there is no market for these
commodities within an economic shipping distance.


17

APPENDIX IL

footage, and percent recover

Diamond drillin,

AANGOOHaHMnKHAKS
aAAANNMNIMMNNSO

Y|
ao) B=)
DUMOCONnNoOoneoesttTOOMNXAHOnNARHROO OOM OSoONNNtONOOCOMY
HIUINOONDNRDONDDOOCFRORODANRNOOOYNDONDANAHOHRDOO AA
Bye SSSSserese ZSaRES ERP SS gages
Sis
AST IATVIISLVIAVIATAIWILARAATMAIYS ANIM MIOQAAMATIS]’ IW MA
as NAAN SGONMAAAN MONA NOD ORIN + NO tO NOI MID
a
uo)
BS eee See STS oo aoa ogo depnancdducdanaly
EI as
aA
enceoeoenmoeceooneoonnnnn reeson4nnwoonen 3
Won MGDOSOHROANNHANOHOHOORN tA OONnHMOMOANHAT 4
ah g 3
eae a ec iar iar tt Ri i ir i i er re hs |
HI NAMNODOVONNROANAVMVDNAHADN Hoonnmamocana
fe mANOOStSTSTTNNOONNODD AANANN OS ST
os .
ck
min +
3
WYAUr~ONRDODOHROONOVONAWSDY NtOoOnnooON
HIOCDDONDONHNDOOHRDHOAAGA ODONDNOODON
eo] 4 a a ae a Lal a aad
Plo
i=
a 80 Sddadedanaggacds esa anase
uo
BRU Sesoeanraaqenenseals esonoonnen
AURORA NTH OHNE t+ ttOO O}F| Faonstaadls
as md le aft
a
o manoooononoonnoece : oonnnonn s
og ANY OOH AHHH ANSS SF tatstonstst :
i) ARANNMNMNMNNONR OH AANNYNYNS SG
3 3 3
Oo} manoooononoonnecye oonnnono
Jeoarcesenenconnecg eonnneng
+
#

Hole |From-| To-

1...



12

FIGURE 5. - Sorting Plant.

The following data pertain to recovery of beryl and mica from the 31
tons processed by hand concentration in the sorting plant:

1. Material processed came from Drift No. 1, in the inner intermediate
zone. The beryl crystals in this zone tend to be larger, therefore more amen-
able to cobbing than the beryl crystals in the other zones.

2. The freshly mined beryl crystals are solidly cemented to the feldspar-
quartz gangue and are much less amenable to cobbing than those from the weath-
ered zone.

3. It is assumed that the beryl content of the 31 tons was comparable to
that of bulk sample No. 7, which assayed 0.065 percent BeO, (equivalent to
0.59 percent beryl). The mica (muscovite) content was estimated at 5 to 10
percent.

4. About seventy-five percent of the pegmatite mined from the zone was
coarse enough for hand concentration.

5. In this coarse fraction, an estimated 30 percent of the beryl and 80
percent of the mica occurred as crystals sufficiently large for hand sorting.


miles north northwest of Drake, which is on U.S. Highway No. 34. U.S. Highway
No. 34, which follows the canyon of the Big Thompson River, is surfaced and
well maintained. The mine can be reached from Drake by driving 0.5 mile west-
ward on State Highway No. 262, then 4.5 miles northward on an unsurfaced moun-
tain road that passes through the Hyatt Ranch. The road to the ranch is rough
and narrow and has steep grades and sharp curves.

The nearest shipping point is 13 miles east of Drake, where a spur of the
Colorado and Southern Railroad crosses U.S. Highway No. 34. Loveland, a town
of 10,000 population and the nearest commercial center, is 22 miles by road
east of the mine and 56 miles north of Denver.

PHYSICAL FEATURES AND CLIMATE

The region adjacent to the mine is a rolling upland dissected by deep,
precipitous canyons. The relief, which is very great near the Big Thompson
River, necessitates circuitous routes for roads in the area. At the mine, the
altitude is 8,100 feet, or nearly 2,000 feet higher than Drake. Storm Moun-
tain, about 2 miles northwest from the mine, has an altitude of 9,915 feet.

Most of the nearby streams are intermittent; the nearest permanent stream
is the North Fork Thompson River, about 1.5 miles to the southwest. A heavy
growth of timber covers the area near the mine.

The climate is generally pleasant in late summer and early fall. At the
altitude of the mine, moderate to heavy snowfall can be expected during the
winter months.

HISTORY, OWNERSHIP, AND PRODUCTION

Mining in the Crystal Mountain district began in 1884 when the Buckhorn
mica mine was discovered. This operation lasted only a few years, but activity
was resumed in 1934 when it was learned that pegmatites in the district con-
tained beryl. In 1941, the United Beryllium Ores and Metals Corp., Denver,
Colo. bought the mineral rights on most of the land in the district to obtain
control of nearly all the pegmatites.

The Hyatt Ranch pegmatite was located in 1936 by Roy Hyatt. In 1936,
Hyatt shipped 1,500 pounds of beryl, of which 1,200 pounds was recovered from
float. The deposit was next located by Fred H. Hyatt who, in September 1942,
leased the property to the above-mentioned United Beryllium Ores and Metals
Corp. The property was operated by this company intermittently in the fall
of 1942 and, under a financial arrangement with the Reconstruction Finance
Corporation, was worked continuously from June to December 1943. During the
latter period, beryl shipped from the property amounted to 34 tons that aver-
aged 11.04 percent BeO and was valued at $4,578.10.

In 1948, Fred H. Hyatt leased the property to Michael D. Lyons who mined
about 400 tons of feldspar and 30 tons of scrap mica in that year. According
to Lyons, the mica was of satisfactory quality, but the feldspar was of poor
quality because it was mined nonselectively.


HYATT RANCH PEGMATITE, LARIMER COUNTY, COLO.-/
by

M. M. Gilkey2/

INTRODUCTION AND SUMMARY

Pegmatites in Colorado occur for 150 miles along the Front Range (eastern-
most range of the Rocky Mountains) from Larimer County on the north to Canon
City on the south, and west into the Gunnison area. Many of the deposits have
been classified. Minerals found in the various dikes include beryl, scrap and
possibly punch mica, lithium-bearing minerals, columbite-tantalite, feldspar,
and several rare minerals.

Pegmatites are abundant in the Crystal Mountain district in Larimer
County. About 5 miles south of the Crystal Mountain district and often iden-
tified with that district is the Hyatt pegmatite area. The Hyatt Ranch deposit
has attracted particular attention because of the comparatively high beryl con-
tent of the upper part exposed in opencut workings.

The Hyatt Ranch pegmatite, at an altitude of 8,100 feet, is in a heavily
wooded region of rough terrain. Access to the property is by 4-1/2 miles of
unsurfaced mountain road that branches from State Highway No. 262 near Drake,
Colo. The climate in the vicinity of the property is characterized by pleas-
ant summers and moderately severe winters.

The deposit was discovered in 1936 and was worked intermittently by sev-
eral operators in 1936, 1942, 1943, and 1948. This work was confined to shal-
low opencut operations. Total recorded production from the deposit is about
50 tons of beryl, 30 tons of scrap mica, and 400 tons of potassium feldspar.

The geologic age of the pegmatite and of the enclosing schist and granite
is Precambrian. The pegmatite strikes northeasterly and dips northwesterly.
It is a roughly lenticular body 365 feet long and has a maximum width of 70
feet. Near its center, it appears to bottom about 200 feet vertically below
its surface outcrop. Besides a discontinuous border zone, it is divided into
four internal zones: A wall zone, outer intermediate zone, inner intermediate
zone, and core zone. Most of the beryl is found in the inner intermediate and
wall zones. Muscovite occurs principally in the inner intermediate zone.

/ Work on manuscript completed January 1960.

1
2/ Mining engineer, Bureau of Mines, Denver, Colo.




13

6. Cobbing of the beryl to a clean product involved loss of about 20 per-
cent of the average crystal. The larger books of mica, however, required
little, if any, cobbing.

7. From the estimated percentage figures in items 4, 5, and 6, it is
calculated that about 18 percent of the beryl and 60 percent of the mica in
the 31 tons of inner intermediate-zone pegmatite were recovered in the sorting
plant.

Although the tonnage processed was small, the results obtained in the
sorting plant warranted the assumption that hand concentration of beryl and
mica from pegmatite mined in the underground part of the deposit was not
economically feasible.

Metallurgical Tests

At the Federal Bureau of Mines laboratory in Rolla, Mo., high-grade con-
centrates and high recoveries have been obtained from beryl ores containing
as little as 0.35 percent BeO. lLower-grade concentrates, but fairly high per-
centage recoveries, have been obtained from ores containing less than this
amount of BeO. The basic flotation procedure was essentially the same as that
developed at the Bureau of Mines laboratory in Salt Lake City, Utah. The two
7-ton samples (Nos. 7 and 8) were sent to Salt Lake City for assaying and
metallurgical testing.

Chemical and microscopic studies revealed that the two samples were simi-
lar in composition and contained about 35 percent quartz, 25 percent ortho-
clase (potassium feldspar), 25 percent plagioclase, and 10 percent muscovite.
Tourmaline, apatite, hornblende, and other minor ferromagnesian minerals com-
posed about 5 percent of the ores. The samples contained no columbite, tan-
talite, spodumene, or lepidolite. The studies showed that beryl and mica were
the only potentially valuable minerals in the samples. The potassium feldspar
was of little value because it was intergrown with both plagioclase feldspar
and quartz. A spectrographic analysis revealed that the mica contained a
minor amount of chemically combined lithium. As shown on figure 3, sample No.
7 assayed 0.065 percent BeO, and sample No. 8 assayed 0.022 percent BeO.

The ore-dressing tests performed on both samples included: (1) hand
sorting of the crushed ores to obtain beryl concentrates, (2) stage crushing
and screening to obtain mica concentrates, and (3) flotation to recover both
beryl and mica.

A plus-90-percent mica concentrate was recovered as a byproduct by stage
crushing and screening. Also effective for concentrating the mica was flota~
tion of finely ground ore. However, the hand-sorting and flotation studies
demonstrated that most of the beryl in the ores is finely crystalline and
difficult to recover. Moreover, the beryl flotation concentrates assayed far
below marketable grade. A description of the metallurgical tests made by
Richard Havens3/ and his discussion of the results are summarized as follows:

5/ Metallurgist, Bureau of Mines, Salt Lake City, Utah.


R.74W. R73 Ww. R.72 W. R.71 W.
(14) RUSTIC

A }
14)
LEGEND f <
X Pegmatite deposit " pes PLace|TM
>
>
8
A CAHORN COLLINS.
HoRSETOOTH {| "4
Crystal x RESERVOIR *
Mount ain~, | X x aS
N | x N.
i
*
H Storm
H tank T.
1 AH Gal vee Meadow’ “| MASONVILLE e
\
\
°
| ‘Hyatt Ranch o
Ie pegmatite )
| >
>
o 1 2 3 4 56
<="SCALEIN MILES
= el
COLORADO T
5
uy RATTLESNAKE 3 N.
| _B RESERVOIR CAMPION
I GARTER
H RESERVOIR
FIGURE 1. -

Location Map, Hyatt Ranch Pegmatite, Larimer County, Colo.




bi f mi
: etal inventions 5643

CALIFORNIA
INSTITUTE OF

SEP 8~ 1960
TECHNOLUGY

GEOLOGY

HYATT RANCH PEGMATITE,
LARIMER COUNTY, COLO.

By M. M. Gilkey

THE BUREAU OF MINES TH ANNIVERSARY

—————
metadc38685 |

UNITED STATES DEPARTMENT OF THE INTERIOR


St
ln V2
EZ

LEGEND

Wall zone: Plagioclase-orthoclase-quartz- muscovite pegmatite
(Upper portion of wall zone contains 25 percent perthite.)

Outer intermediate zone: Perthite-quartz pegmotite

Inner intermediate zone: Plagioclase- orthoclose-quartz-muscovite pegmatite

Gore zone: Perthite
20 9 20 40 60 20, 190

+ xx Biotite granite
‘SCALE IN FEET

Dump
—— Vein CONTOUR INTERVAL 5 FEET

tL Dip or strike

iitti Opencut

FIGURE 2. - Topographic Map, Showing Surface Geology and Mine Workings, Hyatt Ranch Pegmatite,
Larimer County, Colo. Topography and Geology in Part by W. R. Thurston, U.S.G.S.


The Geological Survey made studies of the deposit during the period
1942-44, and the results are presented in Geological Survey Professional Paper
227. Thurston3/ examined the property in 1947, and the Geological Survey ex-
plored the deposit in 1948 by core drilling.

Total recorded production from the Hyatt Ranch pegmatite was approxi-
mately 50 tons of beryl, 400 tons of feldspar, and 30 tons of scrap mica.

DESCRIPTION OF THE DEPOSIT

The following description of the deposit has been taken partly from
Thurston.4/

In the vicinity of the Hyatt Ranch deposit, numerous pegmatite and gray-
granite bodies intrude dark-gray schists that probably belong to the Precam-
brian Idaho Springs formation. In some exposures the granites are cut by the
pegmatites and, hence, are older; both rocks are probably Precambrian in age.
Few of the deposits are beryl bearing. The beryl-bearing Hyatt Ranch deposit
is the only zoned pegmatite in the area.

The Hyatt Ranch pegmatite cuts across a small pluglike mass of gray bio-
tite granite that crops out along the crest of a small anticline in quartz-
mica schist (fig. 2). The main part of the deposit is in granite, but the
northeast and southwest ends of the deposit project into schist. Between the
granite and pegmatite, the contact is somewhat irregular and is locally grada-
tional. In many places at the granite contact the pegmatite has no border
zone. At the contact with the schist, the border zone is well developed, and
the attitude is readily determinable.

The Hyatt Ranch pegmatite is 365 feet long and has a maximum width of 70
feet. It is a roughly lenticular, asymmetrical body whose long axis trends
N. 60° E.; it has an average dip of 60° NW. The northeast end has a flat
plunge to the southwest that steepens in the granite. The southwest end
plunges about 42° northward, so the pegmatite has approximately the shape of
half a lens tapering downward to the northwest. Near its center it appears
to bottom about 200 feet vertically below its surface outcrop; however, the
keel, or bottom edge of the body, is closer to the surface at its northeast
and southwest ends.

Besides the discontinuous border zone, the Hyatt Ranch pegmatite is
divided into the following four zones (figs. 2 and 3):

1. Wall zone: This zone ranges in width from 1 to 60 feet and averages
about 25 feet. It constitutes the bulk of the pegmatite and its upper part
consists of about 50 percent plagioclase and orthoclase, 25 percent perthite,
and 25 percent quartz. In the lower part, the zone consists of 60 percent
plagioclase and orthoclase and 40 percent quartz. The grains average slightly

3/ Thurston, W. R., Pegmatites of the Crystal Mountain District, Larimer
County, Colo.: Geol. Survey Bull. 1011, 1955, pp. 71-88.
4/ Work cited in footnote 3.


Chemical and microscopic studies indicate that beryl and mica are the only
potentially valuable minerals in the deposit. The potassium feldspar present
is of low quality.

Information gained from exploratory diamond drilling done by the Federal
Geological Survey and examination of the surface workings indicated that the
Hyatt Ranch deposit might contain a substantial tonnage of beryl-bearing
pegmatite of a grade sufficiently high to warrant beneficiation. The purpose
of the Federal Bureau of Mines project at the Hyatt Ranch pegmatite was to
investigate the following: (1) Extent, grade, and distribution of beryl and
other economically important minerals, (2) possibilities for selective mining,
(3) feasibility of hand sorting, and (4) amenability of the ore to metallurgi-
cal beneficiation.

Project work began September 18, 1950. During the one-year period ending
Sept. 18, 1951, an adit 272 feet long was driven to explore the pegmatite from
footwall to hanging wall, four diamond-drill holes (Appendix I) totaling
297.5 feet were completed to explore the deposit below the adit level, and a
sorting plant was constructed and operated to investigate the feasibility of
hand concentration of the beryl and mica. Ground conditions encountered in
the granite and pegmatite were generally satisfactory, although the hardness
of the rock slowed drilling. Core recovery (Appendix II) from the diamond-
drill holes averaged 93 percent. The diamond drilling revealed that about
one-half of the deposit lies below the adit level and that the underlying
portion is similar in grade and mineral distribution to the middle portion
penetrated by the adit. The grade is too low for economic operation at
present prices, and selective mining offers no solution. Results of the
attempt to concentrate the beryl and mica by hand sorting were disappointing.
Although 60 percent of the mica in the ore was recovered by hand sorting, only
18 percent of the beryl was recovered by this method.

In June 1953, two 7-ton samples were taken from the adit level for metal-
lurgical testing. One sample, taken in the inner intermediate zone, assayed
0.065 percent BeO (beryllium oxide). The other was taken from the wall zone
and contained 0.022 percent BeO. The results of the metallurgical experiments
were satisfactory for mica but were unfavorable for beryl. The highest grade
beryl concentrate obtained by flotation assayed only 4.5 percent BeO, and the
recovery of beryl was only 45 percent.

ACKNOWLEDGMENTS

Acknowledgment is made to the Federal Geological Survey for cooperation
in supplying geologic information, and particularly to W. R. Thurston from
whose data the description of the deposit and the maps included in this report
were taken in part. For his continuous cooperation, acknowledgment is made
also to Fred H. Hyatt, owner of the deposit.

LOCATION AND ACCESSIBILITY
The Hyatt Ranch pegmatite is in Larimer County, Colo., in the NE1/4NW1/4

sec. 28, T. 6N., R. 71 W., sixth principal meridian (fig. 1). It is approx-
imately 5 miles south of the Crystal Mountain pegmatite district and about 2


16

APPENDIX I

Summary of diamond-drill-hole data

Distance Depth
from |Elevation Total to Size of hole,
Hole |portal, jof collar,| Bearing|Inclination|depth, |granite,| interval, feet
feet feet feet feet
1....] 233.55 8,054.13 |S 65° E -55° 84.0 75.8 |NX-- O- 2.2
BX-- 2.2- 11.0
AX--11.0- 84.0
243.50 | 8,054.18 |N 65° W -40° 44.5 42.8 |BX-- 0 - 44.5
3...) 238.25 8,054.16 | Vertical -90° 107.5 105.8 |NX-- O- 3.0
BX-- 3.0- 10.0
AX--10.0-107.5
207.75 | 8,054.00 |S 65° E ~35° 61.5 55.1 |BX-- O- 3.0

AX-- 3.0- 61.5



This publication has been cataloged as follows:

Gilkey, Millard M
Hyatt Ranch pegmatite, Larimer County, Colo. [Washington]
U. S. Dept. of the Interior, Bureau of Mines [1960]

18 p. illus., maps, tables. 27 cm. (U.S. Bureau of Mines. Report
of investigations, 5643)

1, Pegmatites—Colorado—Larimer Co. I. Title. (Series)

(TN23.U7 no. 5643] 622.06173

U. S. Dept. of the Int. Library



WORK BY BUREAU OF MINES

Bureau of Mines work on the Hyatt Ranch pegmatite was done during two
periods of operation. Most of the work was accomplished from September 18,
1950, to September 18, 1951. After a 21-month recess, a small amount of addi-
tional work (to obtain bulk samples) was done in the period June 7 through
June 23, 1953.

Preparatory Work

Preparatory work starting on September 18, 1950, included the following:
(1) The repairing of a 4.5-mile access road to the property, (2) removal of
talus and dump material from the site of the adit portal, (3) excavation and
leveling of ground near the portal for a mine yard and surface plant, (4) con-
struction of detonator and explosive magazines and a miners' change house, and
(5) installation of shop equipment, a 315-c.f.m. compressor, and a 500-gallon
gasoline storage tank.

The Adit

From a conveniently situated portal site, an adit was driven N. 65° W.,
or obliquely to the strike, to explore the part of the deposit that directly
underlies the best beryl showing in the surface pit (fig. 2). The elevation,
determined from geologic information available at the time, was designed to
place the adit just below the outer intermediate zone. At that elevation, it
would have been driven through the deposit entirely in wall-zone pegmatite.
However, as shown in figure 3, the adit as driven penetrated the pegmatite some
70 feet above the intended level.

In the vicinity of the portal (fig. 4), the adit is in badly fractured
schist. At 37 feet from the portal it penetrates dense gray granite, and at
154 feet it intersects the footwall of the pegmatite. It intersects the
hanging-wall contact of the pegmatite at 262 feet from the portal and ends in
the granite hanging wall at 272 feet. Timber was required to support the
loose ground near the portal, but no timber was needed beyond the first 20
feet. The cross section of the untimbered portion of the adit is 6 by 7 feet.

Because of the hardness of the granite and pegmatite, most of the blast-
hole drilling in the adit was done with a column-mounted drifting machine. A
30- to 35-hole, 6-foot, burn-cut round gave an average advance of 5 to 5-1/2
feet. The broken rock was mechanically loaded into 16-cubic-foot mine cars
that were hand trammed to the surface. Time used in completing the cycle
ranged from 10 to 16 hours. The project was operated on a one-shift basis.
Miners were paid $1.35 per hour, and underground laborers were paid $1.29 per
hour. The total direct cost averaged $16.41 per foot of advance.

Sampling on Adit Level
Six channel samples, Nos. 1 through 6, were cut from the 16 feet of wall-

zone pegmatite exposed in the adit on the footwall side of the deposit. The
locations of these samples and BeO assay results are given on figure 3. The


1L

Diamond Drillin;

In August 1951, four diamond-drill holes totaling 297.5 feet were com-
pleted to determine the downward extent of the pegmatite, exposed for 108 feet
in the diagonally driven adit, and to obtain samples of the pegmatite below the
adit level (fig. 3). All four holes were drilled in the plane of the vertical
section of the adit. The core from the holes provided information for the
downward projection of the pegmatite zones, and samples for chemical assay and
spectrographic analysis.

All core recovered from the inner intermediate and wall zones, as well as
the core from the core zone of hole No. 1, was split; half was retained for
Bureau of Mines core storage, and half was sent to the Bureau of Mines labora-
tory at Salt Lake City, Utah. Sample length was controlled by zoning. Loca-
tions of the individual samples and results of the chemical assays for BeO
are given in figure 3. Results of the spectrographic analyses are given in
Appendix III.

Chemical assays of the five inner intermediate-zone samples range from
less than 0.005 percent BeO to 0.152 percent, and their weighted average is
0.097 percent BeO. Assays of the four wall-zone samples range from 0.026 per-
cent BeO to 0.092 percent, and the average is 0.052 percent. The one core~zone
sample assayed 0.090 percent BeO but was probably higher in grade than the
core zone would average. The weighted average for all ten diamond-drill-core
samples is 0.067 percent BeO.

Diamond drilling was done on a single-shift basis. Two drill stations
were prepared by raising the back of the adit to a height of 11 feet above
the track. Holes 1, 2, and 3 were drilled from station 1, and hole 4 was
drilled from station 2. The drilling rate in the hard, relatively unfrac-
tured pegmatite and granite was slow, and bit wear was excessive. A total
of 23 shifts was required to complete the four holes. The drilling rate dur-
ing the 19-1/4 shifts spent in actual drilling operations averaged 15-1/2 feet
per shift. Core recovery ranged from 90 to 96 percent for the individual
holes and averaged 93 percent for the 297.5 feet of drilling.

Results of the diamond drilling show that in the vertical plane of the
adit at least half of the pegmatite lies below the level of the adit. The
keel of the pegmatite appears to be about 115 feet below that level. Exam-
ination of the drill core confirmed that the outer intermediate zone--easily
recognized by its high quartz content--is almost entirely confined to the
hanging-wall side of the deposit. The wall zone constitutes the bulk of the
deposit, particularly below the adit level. The pegmatite is further charac-
terized by gradation at its zonal contacts.

Sorting Plant

A sorting plant (fig. 5), constructed adjacent to the mine dump, was com-
pleted in July 1951. Only 31 tons of pegmatite was processed in the plant
before the project work was suspended. The results were unfavorable.


HYATT RANCH PEGMATITE,
LARIMER COUNTY, COLO.

By M. M. Gilkey

» oo * * © » © » & » & — report of investigations 5643

UNITED STATES DEPARTMENT OF THE INTERIOR
Fred A. Seaton, Secretary

BUREAU OF MINES
Marling J. Ankeny, Director






= fo}
By ee
« Sai
St oi
3 38
8 oe
2, \ hart)
«| Se
\
\
\
2 S6 S
D.D. Hole No. g ane, >
445 (-40°) *h LIN AST SY
» kD.D. Hole No. 4 ion of wall-zone samples
Rea teN Soy ee Location of $i-S6 np
opis 06 ee —_—--_+— El. 8 000
th
pens D.D. Hole No. | 84.0! (-55)
trys
OY BERYL SAMPLE DATA
KA
rs SAMPLE LENGTH]  8e0, LEGEND
VAR aM No | TYPE [eeer '|PERCENT| ; ;
SAAD Te St IGhannel| 5.0 {0.07 | Wall zone! Plagioclase- orthoclase-quartz-muscovite pegmatite
WAT Hl SA $6—{Ghonnet 3.6 98 (Upper portion of wall zone contains 25 percent perthite.)
Varn, fs $4__|Channel| 5.0 10 Outer intermediate zone: Perthite-quartz pegmatite
x STRAY D. D, Hole No. 3 5 IC anne 6.0 82 | . . - it egmatite
Ney % 107.5' (-90°) $6 _{Ghannel{ 6.0 Inner intermediate zone: Plagioclase-orthoclase-quartz-muscovite peg
ee S7_[Buk(7T)| 8.0 (o HF . j
85 Bulk PT 22 0 O82 [22%] Gore zone: Perthite
$2" [pDcore| 6.9 “355 +o Biotite granite
Si core! 21! __.090_} =
$i |D.D.corel 12.7 152 Dump
$i2—|D.0-core| 35:6 026
$13 |D.D.core| 37.5 “052
$14 |D:D.core| 25.8 12
Si5___|D.D.core| 38.0 09
S16 _|D:D.corel 1.0 |< 905 |
Si7__|0.D.corel 6.5 < 005 _|
S18 |0.0.core| 26.3 030
20 io} 20 40 60 80 100

SCALE IN FEET

FIGURE 3. - Longitudinal Section Through Adit, Showing Zoning and Sample Locations, Hyatt Ranch Pegmatite,
Larimer County, Colo. Geology in Part by W. R. Thurston, U.S.G.S.



10

FIGURE 4. - View of Adit Portal and Adjacent Area.

six assays average 0.05 percent BeO, which is equivalent to about 0.45 percent
beryl.

Also shown on figure 3 are the locations and assay results for two bulk
samples, Nos. 7 and 8. These two samples, for metallurgical testing, were
obtained in June 1953 when the project was reactivated for the purpose of
additional sampling. Both were taken on the hanging-wall side of the deposit.

Sample No. 7 consisted of 7 tons of pegmatite from Drift No. 1, driven
north-easterly in the inner intermediate zone. Every third car of the rock
broken in 8 feet of advance was saved for the sample, which assayed 0.065 per-
cent BeO. The drift was extended to a total distance of 28 feet from the adit
to obtain further information regarding the composition of the zone. Inspec-
tion revealed that the part of the inner intermediate zone penetrated by the
drift is highly irregular in composition.

Sample No. 8 assayed 0.022 percent BeO and consisted of 7 tons of peg-
matite from the wall zone exposed on the north side of the adit. The excava-
tion for the sample measured 2 by 7 by 22 feet and extended the full length
of the wall-zone exposure. Approximately one-third of the broken material was
saved for the sample. The wall zone (on both the hanging-wall and footwall
sides of the deposit) is comparatively uniform in composition.