|

The following are selected text excerpts from the November
6, 2000 Petrographic Report on 25 Polished
Thin Sections by Vancouver Petrographics Ltd. on the
Alto de Lipangue gold/copper property.
The complete report is available for viewing at the corporate
offices of
Medinah Mining, Inc.

PETROGRAPHIC
REPORT ON 25 POLISHED THIN SECTIONS
LIPANGUE AND LAS DOS MARIAS GOLD-COPPER
PROPERTIES
METROPOLITAN REGION, CHILE
FOR
Medinah Mining, Inc.
Report for: Les Price
Medinah Mining, Inc.
302-255 West 1st Street
North Vancouver, B.C.
V7M 3G8
November. 6, 2000.
SUMMARY:
The rocks in this suite
of samples are mainly strongly altered, making recognition
of primary lithology difficult. The first five samples, from
113 to 190 m, and the last sample at 325m, still display recognizable
texture. In the upper 190 m, three of the samples (113, 170,
and 190 m) appear to be a porphyritic to hypidiomorphic, clinopyroxene-?hornblende
(or clinopyroxene-?orthopyroxene) bearing diorite to monzodiorite
or (less likely) noritic leucomonzogabbro. The latter classification
would result if the relict altered mafic in these rocks was
orthopyroxene. These rocks are composed of seriate-textured
to porphyritic oligoclase-andesine, clinopyroxene, and relict
?hornblende or ?orthopyroxene, now pseudomorphed by amphibole
and chlorite, in a matrix of K-feldspar and minor quartz.
The samples from 175 and 179 m differ in containing significant
quartz (possibly mainly secondary in the former, but distinctly
phyric and primary in the latter); these smaples, particulary
the latter, could represent crystal-lithic tuffs. The last
sample, from 325 m, is a seriate-textured quartz monzonite;
note that since the amount and style of quartz in this sample
are somewhat similar to that of quartz in many of the altered
rocks higher up in the hole, it is possible that this could
be a protolith for those samples. However, it appears to be
somewhat less mafic than most of them, suggesting that a diorite
or quartz diorite rather like that from 113.70 m or 317.35
m could also be a viable protolith.
There appears to be an
increase in level of alteration in the sequence from about
200 m on, with increasing ?early potassic K-feldspar and quartz
alteration replacing ?plagioclase, culminating in quartz-sulfide
stockwork at 221-225 m and again around 290-310 m and 320-325
m. It is not clear that all or even most of the K-feldspar
in these rocks is secondary since it is only rarely observed
to be directly controlled by fractures or veins. Also, the
presence of abundant primary or late-magmatic K-feldspar in
the sample from 325 m, coupled with the difficulty of recognizing
the primary lithology in these strongly altered rocks, raises
the possibility that some or most of the disseminated K-feldspar
is primary, derived from a rock such as the quartz monzonite
at 325 m. However, against these arguments must be set the
overall observation that K-feldspar is most abundant in the
zone of most altered rocks (this can best be seen by laying
out the stained offcuts).
Most of these (?potassic)
altered rocks are also overprinted by an episode of phyllic
(clay-sericite-chlorite-rutile, + quartz, calcite to
?ankeritic carbonate, sulfides) or locally ?advanced argillic
alteration (possibly including ?pyrophyllite in addition to
the phyllic mineral assemblage) that may be later than or
?partly synchronous with the ?potassic alteration. Outside
the (?potassic)-phyllic zone (i.e. above 200 m, below 325
m and possibly in one sample from 299 m), alteration is mainly
propylitic (chlorite-epidote-calcite) to transitional "mafic
potassic"-propylitic (amphibole, alkali feldspar including
K-feldspar, quartz, magnetite, sphene, apatite). Note that
magnetite, common in the upper part of the hole, is destroyed
in the central and lower parts of this zone (magnetite occurs
from 170 to 213 m except for the crystal tuff at 179 m, and
then not again until the last sample from 325.60 m).
Sulfides are mainly pyrite
with minor to trace chalcopyrite and rare bornite; traces
of Fe-poor (colourless) sphalerite, containing myriads of
microscopic chalcopyrite blebs, are found in two samples (224
and 231 m); galena is found with sphalerite in 224 m. Chalcopyrite
has more limited distribution than pyrite, and is commonly
found associated with pyrite only in the vein or fracture
zones in the sample rather than with the disseminated pyrite.
Chalcopyrite is really only abundant in one very mafic sample
(massive chlorite+calcite-quartz-rutile from 299 m).
The bornite occurs in only one sample, from 175 m, also a
relatively mafic rock altered to a ?skarn or "mafic potassic"
assemblage including clinopyroxene, calcic plagioclase, epidote,
quartz, magnetite, sphene and apatite.
Craig H.B. Leitch, Ph.D. P.Eng
492 Isabella Point Road,
Salt Spring Island, B.C. Canada
V8K 1V4
L00-13-113.70: PROPYLITIC-?POTASSIC (CHLORITE-KSPAR-EPIDOTE-CALCITE-AMPHIBOLE)
ALTERED HORNBLENDE PYROXENE DIORITE OR ?NORITIC LEUCO-GABBRO
Hand sample is a grey-green,
medium-grained intrusive rock of intermediate composition
(mainly plagioclase and relict mafic minerals). The rock is
not magnetic, but shows minor reaction to cold dilute HCl;
minor yellow stain in the etched slab suggests K-feldspar
replaces plagioclase. Modal mineralogy in polished thin section
is approximately:
|
Plagioclase (?oligoclase)
|
45%
|
|
Chlorite
|
25%
|
|
K-feldspar (after plagioclase)
|
10%
|
|
Quartz (?partly secondary)
|
5%
|
|
Clinopyroxene
|
5%
|
|
Epidote, zoisite
|
5%
|
|
Amphibole (partly secondary)
|
1-2%
|
|
Carbonate
|
1-2%
|
|
Sphene, rutile, ilmenite
|
1-2%
|
|
Apatite
|
<1%
|
This sample is composed
mainly of altered plagioclase and lesser elongated relic mafics,
with a holocrystalline texture. Scattered opaques are mainly
sphene and rutile.
Plagioclase
about An25-30 forms mainly euhedral crystals up to 1.5 mm
in diameter that are moderately altered (20-40% replaced)
by epidote and by innumerable microfractures of K-feldspar
or rare carbonate. Minor quartz, likely partly primary, forms
irregular crystals up to 0.5 mm across in interstitial positions
or partly intergrown with/replacing plagioclase.
There
appear to have been at least two mafic minerals present. Relict
clinopyroxene has euhedral outlines up to 1.5 mm in size,
now partly replaced by zoisite and pale-coloured secondary
amphibole plus lesser carbonate (likely calcite). Possible
former ??orthopyroxene or ?amphibole now occurs as euhedral
relics up to 1.5 mm long completely pseudomorphed by fine-grained
chlorite, possibly with "hydrobiotite". Minor pale-coloured
amphibole, likely secondary, is also associated with the latter
mafic relics. The pseudomorphs have extinction parallel to
their length and to the fibres of the chlorite, square cross-sections,
and contain minute crystals of rutile. Larger aggregates of
rutile in the cores of sphene aggregates up to 0.6 mm in diameter,
are probably after original ilmeno-magnetite, of which rare
tabular crystals up to 0.5 mm remain. Interstices between
plagioclase and euhedral mafics are also filled by a second
variety of chlorite.
In summary,
this appears to have been a pyroxene-hornblende diorite or
possibly leucocratic gabbro (even noritic gabbro if it did
contain orthopyroxene rather than amphibole, as well as clinopyroxene).
Original quartz content was probably less than 5%; the plagioclase
composition may have been more calcic. Alteration is moderate
propylitic or ?transitional potassic (chlorite/hydrobiotite,
K-feldspar, epidote, amphibole, carbonate, quartz, rutile),
but there is no sulfide. The K-feldspar could be late magmatic
rather than hydrothermal in origin.
L00-13-170.00:
WEAK PROPYLITIC (CHLORITE-EPIDOTE-SPHENE/RUTILE) ALTERED,
PORPHYRITIC ?PYROXENE MONZODIORITE OR ??NORITIC LEUCOGABBRO
Hand sample is a fine-grained,
dark grey-green, slightly altered vaguely porphyritic intrusive
rock. The rock is weakly magnetic but shows no reaction to
cold dilute HCl, and minor yellow stain for K-feldspar in
the etched slab. Modal mineralogy in polished thin section
is approximately:
|
Plagioclase (?andesine)
|
60%
|
|
Clinopyroxene (?augite)
|
10%
|
|
Amphibole (partly secondary)
|
10%
|
|
K-feldspar (matrix)
|
10%
|
|
Chlorite
|
5%
|
|
Epidote, zoisite
|
2-3%
|
|
Sphene, rutile
|
1-2%
|
|
Magnetite
|
<1%
|
|
Chalcopyrite
|
tr
|
This slide consists of
about 25% scattered plagioclase and 10-15% glomeratic clinopyroxene
phenocrysts in a fine-grained groundmass.
Plagioclase phenocrysts
(An45) are euhedral, up to 5 mm long, and show minor alteration
to epidote/zoisite plus fracturing by a low-relief mineral
(?Kspar or zeolite). Some crystals are strongly zoned, with
narrow rims of ?oligoclase (see photomicrograph).
Clinopyroxene phenocrysts
have euhedral but ragged (corroded) outlines up to 2 mm in
diameter and are mantled by pale olive green amphibole (?hornblende)
in parallel position. A separate type of relict mafic forms
smaller crystals with euhedral outlines up to 1 mm in diameter,
pseudomorphed by either secondary amphibole or chlorite-hydrobiotite
as in the sample from 113.70. It is not clear if these were
originally hornblende or ?orthopyroxene; the latter is suggested
by the fact that they are more altered than the clinopyroxene
in the same sample, and there is unaltered amphibole present
in the section.
Scattered aggregates
of sphene up to 0.7 mm across, commonly cored by minute crystals
of rutile, likely represent the sites of former ilmenite;
they are locally associated with euhedral magnetite to 0.4
mm in diameter, and trace chalcopyrite up to 75 microns long.
Very rare chalcopyrite also forms minute blebs included in
plagioclase.
The groundmass consists
of euhedral plagioclase microlites, mainly <0.25 mm long
but in places with a tendency to seriate texture (crystals
up to 0.5 mm), with lesser euhedral clinopyroxene (<0.1
mm long), subhedral amphibole (<0.15 mm), and interstitial
K-feldspar, chlorite, epidote and opaque oxides of finer grain
size.
The ratio of total plagioclase
to total feldspar of about 0.85 indicates that this rock may
be classified as a porphyritic pyroxene monzodiorite (could
have been leucocratic noritic monzogabbro if ?orthopyroxene
were initially present). Alteration is propylitic, to chlorite-epidote-sphene/rutile
+ trace chalcopyrite.
L00-13-174.9: SKARN OR
"MAFIC POTASSIC" (CLINOPYROXENE-PLAGIOCLASE-QUARTZ-
EPIDOTE-APATITE-MAGNETITE-CHALCOPYRITE+BORNITE) ALTERED,
QUARTZ-PHYRIC INTRUSIVE OR VOLCANIC ROCK
Hand sample is a mottled,
grey-green, fine- to medium-grained, altered intrusive rock.
Fine sulfides, including chalcopyrite (asociated with magnetite),
accompany the mottling and a pale creamy-coloured, fracture
controlled alteration that surrounds darker, rounded mottles.
There is trace reaction to cold dilute HCl along hairline
fractures, but no stain for K-feldspar in the etched slab.
Modal mineralogy in polished thin section is approximately:
|
Plagioclase (?oligoclase, largely secondary)
|
35%
|
|
(relict labradorite)
|
5%
|
|
Clinopyroxene (?diopside; secondary)
|
35%
|
|
Quartz (?largely secondary except phenocrysts)
|
15%
|
|
Magnetite
|
5%
|
|
Epidote
|
1-2%
|
|
Chalcopyrite
|
1%
|
|
Sphene
|
1%
|
|
Bornite
|
1%
|
|
Apatite
|
1%
|
This slide consists mainly
of a fine-grained intergrowth of clinopyroxene, plagioclase
feldspar, quartz and magnetite averaging about 0.15 mm or
less in diameter, and containing scattered quartz crystals
with euhedral to subhedral outlines up to 1.5 mm in diameter.
Rarely, remnants of twinned calcic plagioclase phenocrysts
(An60) up to 1.5 mm long are visible.
The dark mottles, possibly
representing sites of former mafic crystals, are now composed
mainly of clinopyroxene (pale green ?diopside rarely over
0.1 mm in diameter), commonly with minor sphene of <30
microns diameter. The creamy-coloured areas surrounding the
mottles appear to be composed mainly of secondary alkali feldspar,
possibly of oligoclase composition to judge by the relief
against quartz, and lesser pyroxene and quartz, all forming
subhedra mainly <0.2 mm in size.
The dark mottles are
generally centered on areas of disseminated or clotty magnetite,
in places with associated sulfides, significant epidote and
minor apatite. Magnetite forms subhedra generally <0.35
mm in diameter; chalcopyrite forms subhedra of similar size
in places intergrown with bornite of similar size. Epidote
forms subhedra up to 0.1 mm in size with pale yellow pleochroism
indicating relatively low Fe, high Ca content; apatite forms
subhedra to 0.2 mm in aggregates to 1 mm across. The lack
of pyrite, presence of bornite with chalcopyrite suggest a
low sulfide, low total sulfur part of a porphyry copper system,
commonly found associated with magnetite.
Although remnants of
the original ?intrusive or volcanic rock can be seen in places
in the slide, this is clearly a strongly altered rock. Presence
of phenocryst quartz suggests the protolith was different
in composition from the samples at 113/170 m, more like the
sample from 178.6. The alteration, to pyroxene, plagioclase,
quartz, epidote, apatite, magnetite and copper sulfides, suggests
a skarn or an unusual type of "mafic potassic" alteration
in an island-arc porphyry copper system (somewat similar alteration
is seen in some zones at Island Copper, B.C. and the Tanama
and Helecho deposits in Puerto Rico).
L00-13-178.6: ?PROPYLITIC
(ALKALI FELDSPAR-?QUARTZ-CARBONATE-EPIDOTE- CHLORITE-ZEOLITE-SPHENE-APATITE)
ALTERED ?CRYSTAL LITHIC TUFF
Hand sample is a pale
creamy to greenish coloured, medium-grained, felsic rock containing
abundant crowded lithic clasts and crystal shards with a jumbled
appearance like a crystal-lithic tuff, cut by a sheeted system
of pale greenish-white veinlets. The rock is not magnetic
but shows strong reaction to cold dilute HCl, and some yellow
stain for K-feldspar in the etched slab. Modal mineralogy
in polished thin section is approximately:
|
Quartz (partly secondary)
|
50%
|
|
Plagioclase (?partly secondary)
|
25%
|
|
K-feldspar (in clasts)
|
10%
|
|
Carbonate (mainly calcite, veins)
|
5-7%
|
|
Epidote
|
3-5%
|
|
Chlorite
|
2-3%
|
|
?Zeolite
|
1-2%
|
|
Sphene
|
1-2%
|
|
Apatite
|
<1%
|
This slide is composed
of tightly packed, abundant silicic-feldspathic lithic clasts
mostly <0.5 cm in diameter and scattered quartz crystals
or aggregates (?recrystallized crystals) mostly <2 mm in
diameter. The rock is clast-supported, with very little matrix
recognizable between the clasts.
The lithic clasts are
composed mainly of either fine-grained quartz (probably mostly
secondary; remnants of former plagioclase barely visible in
some) or alkali feldspar and quartz. The latter commonly stain
yellow in the etched slab, indicating that significant K-feldspar
is present, which could be secondary (associated with the
vein zone crossing the sample) but this is not obvious. Grain
size form both quartz and feldspar in the clasts is generally
<0.1 mm.
Clots of alteration minerals
with irregular outlines up to about 1.5 mm across are composed
of epidote, chlorite, apatite, carbonate and ?zeolite; relict
plagioclase in some suggests they may be after former calcic
plagioclase, but abundant sphene in others suggest derivation
from former mafic crystals such as ?pyroxene. Negative relief
of the plagioclase against quartz suggests it may be sodic
(?oligoclase or albite), and in part secondary. It is not
clear how much of the quartz is secondary, given the abundant
quartz in many of the clasts.
Veins, up to about 1
mm thick, are composed mainly of carbonate (likely mostly
calcite, subhedra to 0.5 mm) with minor epidote (subhedra
<30 microns) and quartz (euhedra to 0.2 mm). In places
the veins contain central fillings
In summary, strong propylitic
alteration to alkali feldspar (mainly sodic, but possibly
also including Kspar), epidote, chlorite, carbonate, zeolite,
sphene, apatite, and possibly quartz, has made it difficult
to guess the original protolith for this crystal-lithic tuff.
It may have been of felsic to intermediate composition, depending
on how much mafic material was present.
L00-13-190.4: WEAK PROPYLITIC
(AMPHIBOLE-CHLORITE-EPIDOTE-CALCITE) ALTERED, PORPHYRITIC
?PYROXENE MONZODIORITE (OR ??NORITIC LEUCOGABBRO)
Hand sample is dark grey-green,
fine-grained, massive porphyritic mafic to intermediate high-level
intrusive rock. The rock is weakly magnetic, reacts to cold
dilute HCl along narrow fractures, and shows minor yellow
stain for K-feldspar in the groundmass of the etched slab.
Modal mineralogy in polished thin section is approximately:
|
Plagioclase (andesine-oligoclase)
|
65%
|
|
Clinopyroxene (?augite)
|
10%
|
|
K-feldspar (groundmass)
|
10%
|
|
Amphibole (mainly secondary)
|
5%
|
|
Chlorite
|
5%
|
|
Magnetite
|
1-2%
|
|
Sphene, rutile
|
1%
|
|
Quartz
|
1%
|
|
Carbonate (calcite)
|
1%
|
|
Epidote
|
<1%
|
This slide is composed
mainly of plagioclase and lesser clinopyroxene with a seriate
to porphyritic texture. Plagioclase forms euhedral crystals
ranging from phenocrysts up to 3 mm long down to groundmass
crystals of less than about 0.5 mm, but ranging from 0.1 to
almost 1 mm long. Plagioclase phenocrysts are zoned, with
cores about An40 and rims about An20; alteration to epidote
and carbonate is rare. Clinopyroxene forms euhedral phenocrysts
(also oscillatory zoned) up to 2 mm long and smaller seriate
subhedra mostly <0.5 mm in diameter. Pyroxene is occasionally
rimmed or intergrown with olive-green amphibole subhedra up
to the size of the pyroxene.
Interstices between plagioclase
crystals are filled with small (mainly <0.3 mm diameter)
subhedral altered mafic relics and 0.1 mm magnetite plus a
mesh of anhedral K-feldspar to 0.15 mm, and minor sphene (subhedra
to 50 microns, containing minute ?rutile) and quartz (irregular
anhedra to 0.1 mm). The mafic relics are altered at the core
to pale green chlorite, but the rims appear to be fibrous,
olive-green to brownish ?secondary amphibole, plus minor epidote.
Rectangular to square outlines suggest they could have been
?orthopyroxene; minor non-fibrous, fresh olive-green amphibole
forming subhedra to 0.25 mm intergrown with the relics argues
against the mafic relics having originally been hornblende.
However, lath-shaped mafic relics partly replacing clinopyroxene,
and now composed of clear, subhedral or in places fibrous
secondary amphibole, show that hornblende is present. Thus
the question of original ?orthopyroxene remains open.
In summary, this appears
to represent a porphyritic pyroxene monzodiorite (or noritic
leucogabbro if there originally was orthopyroxene present),
with similarities to the sample from 170.0 m. Alteration is
weak propylitic (secondary amphibole, chlorite, epidote, carbonate,
sphene).
L00-13-212.0: PHYLLIC
(SERICITE-CHLORITE-PYRITE-RUTILE), POSSIBLY EARLIER POTASSIC
(KSPAR-CHLORITE-MAGNETITE) ALTERED ?CRYSTAL TUFF
Hand sample is pale grey-green,
fine-grained, massive, altered ?porphyritic felsic-intermediate
?volcanic or intrusive rock with small vugs and fine disseminated
pyrite. The rock is slightly magnetic, shows no reaction to
cold dilute HCl, but stains extensively for K-feldspar in
the etched slab. Modal mineralogy in polished thin section
is approximately:
|
Plagioclase (relict)
|
45%
|
|
Sericite, ?clay
|
20%
|
|
K-feldspar (?partly secondary)
|
15%
|
|
Chlorite
|
10%
|
|
Quartz (?mainly primary)
|
5-7%
|
|
Pyrite, trace chalcopyrite
|
1-2%
|
|
Magnetite
|
1%
|
|
Rutile, sphene
|
1%
|
|
Apatite, zircon
|
<1%
|
This sample consists
of variably altered plagioclase, relict mafic sites, and scattered
quartz (?relict phenocrysts or shards). Although it is difficult
to be sure due to the alteration, there is a vaguely tuffaceous
texture to the rock.
Plagioclase appears to
have formed sub- to euhedral crystals up to about 3 mm long
that are now extensively replaced by fine-grained clay-sericite
(flakes to 50 micron size) and, in many places, apparently
by K-feldspar. The K-spar replacement is earlier than the
clay-sericite, and spreads along cleavages throughout the
plagioclase crystal, leaving vaguely twinned remnants. The
K-feldspar could have been late magmatic in origin since it
does not appear to be related to fractures or veins, or it
may be hydrothermal, related to a structure larger than the
scale of the hand specimen. Kspar also appears to form smaller
crystals mixed with minor quartz as groundmass crystals that
may be ?primary.
Mafic relics have subhedral
outlines up to 1.5 mm long that are permissive of former ?pyroxene
or amphibole. They are pseudomorphed by fine-grained (<0.1
mm) pale green chlorite and minor sericite, plus traces of
rutile, sphene, magnetite and pyrite. Rare small apatite euhedra
are up to 0.1 mm long, and rare euhdral zircon are <75
microns long. Euhedral to subhedral magnetite crystals are
mainly <0.2 mm in size. Rutile forms subhedral aggregates
up to 0.85 mm across of minute euhedra. Scattered euhedral
pyrite crystals are mostly <1 mm in diameter; rare chalcopyrite
up to 40 microns in diameter is associated with chlorite.
It is not clear what
the protolith for this phyllic (sericite-chlorite-pyrite-rutile+sphene)
altered rock was; also, there may have been minor potassic
(Kspar-magnetite) alteration prior to phyllic alteration,
which the chlorite would fit better with. It is vaguely tuffaceous
or porphyritic, and contains phyric quartz like samples from
174.9 and 178.6; it may have been a crystal tuff of intermediate
composition.
L00-13-213.0: PHYLLIC
(SERICITE-CHLORITE-CARBONATE-PYRITE-RUTILE), POSSIBLY EARLIER
POTASSIC (QUARTZ-KSPAR-?MAGNETITE) ALTERED ?CRYSTAL TUFF
Hand sample is grey-green,
massive,medium-grained, vaguely tuffaceous or porphyritic
?volcanic or intrusive rock, slightly bleached towards a fracture
coated with white sericite or ?clay. The rock is weakly magnetic,
shows strong reaction to cold dilute HCl, and strong yellow
stain for K-feldspar in the etched slab. Modal mineralogy
in polished thin section is approximately:
|
K-feldspar (?largely secondary)
|
35%
|
|
Quartz (?partly secondary)
|
25%
|
|
Relict plagioclase
|
10%
|
|
Sericite, ?clay
|
10%
|
|
Chlorite
|
10%
|
|
Carbonate (partly calcite)
|
5-7%
|
|
Magnetite
|
1%
|
|
Rutile
|
1%
|
|
Pyrite
|
<1%
|
This sample consists
mainly of relict altered feldspars, relict mafic sites, and
quartz. The alteration is intense enough to conceal primary
textures, so that it is not clear whether it is a crystal
tuff or a porphyritic intrusive.
Relict feldspar crystals
have euhedral to somewhat ragged outlines up to almost 3 mm
long. Vaguely defined relict twinning and the shapes suggest
most were probably originally plagioclase; however, most are
now replaced by secondary alkali feldspar that stains yellow
for K-spar in the etched slab. Most of this secondary alkali
feldspar is also altered by fine-grained sericite or clay,
but this appears to be an overprint. The K-feldspar is not
clearly secondary hydrothermal in origin (not related to veins
or fractures); it could be late magmatic, or the controlling
structure could be larger than the scale of the hand specimen
available.
Quartz is abundant, forming
mainly subhedral to anhedral crystals up to about 1 mm in
diameter that poikilitically enclose other crystals and commonly
have overgrowth rims, suggesting some may be secondary in
nature. Again, as for K-spar, the period of quartz overgrowths
may have been late magmatic rather than hydrothermal. Narrow
quartz veinlets <0.1 mm thick are rare, but in places they
grade into irregular areas of fine-grained quartz in a reticulate
network.
Relict mafic sites with
non-definitive ragged, irregular outlines mostly less than
1 mm in diameter, are pseudomorphed by chlorite, carbonate
(possibly calcite and ?ankerite), sericite and rutile, or
less commonly magnetite or pyrite. Cores of the pseudomorphs
tend to be chlorite and minor sericite; rims tend to be carbonate.
Rutile aggregates may be up to 1 mm across, composed of minute
<30 micron crystals. Magnetite forms subhedra up to 0.25
mm in diameter; pyrite euhedra are mainly <0.15 mm in diameter.
This sample appears to
represent a ?crystal tuff (or ?high-level porphyritic intrusive)
of intermediate composition that has undergone extensive replacement
by quartz and Kspar (magnetite may be partly secondary and
have formed during this stage), followed by phyllic alteration
to sericite, chlorite, carbonate, pyrite and rutile.
L00-13-215.95: PHYLLIC
(SERICITE-CHLORITE-PYRITE-SPHENE/RUTILE), POSSIBLY EARLIER
POTASSIC (KSPAR-QUARTZ) ALTERED ?CRYSTAL TUFF
Hand sample is grey-greenish
to creamy-buff in colour, fine- to medium-grained, with an
altered ?porphyritic or tuffaceous texture, minor irregular
quartz veins, and disseminated sulfides. The rock is not magnetic
and shows no reaction to cold dilute HCl, but there is abundant
stain for K-feldspar in the etched slab. Modal mineralogy
in polished thin section is approximately:
|
K-feldspar (?largely secondary)
|
45%
|
|
Quartz (partly secondary)
|
25%
|
|
Sericite, ?clay
|
20%
|
|
Chlorite
|
5%
|
|
Pyrite
|
3-5%
|
|
Sphene, rutile
|
1-2%
|
|
Zircon
|
tr
|
This slide is similar
to the previous slide, composed of abundant relict K-feldspar,
lesser quartz, sericitized relict ?plagioclase sites, and
minor chlorite, pyrite and sphene/rutile after mafic minerals.
It is so strongly altered that the original texture is difficult
to discern, suggestive of either a crystal tuff or a porphyritic
high-level intrusive rock.
Sericite (and ?clay)
altered plagioclase sites have subhedral outlines up to 0.5
cm long that are pseudomorphed by 10-20 micron flakes. Other,
vaguely defined sites of similar shape and size appear to
be replaced by K-feldspar, quartz and sericite. The K-feldspar
forms subhedral crystals mainly <0.5 mm in diameter, themselves
partly replaced by fine subhedral flakes of sericite. In places
what appears to be relict twinning, mimicked by lath-shaped
Kspar and quartz, suggests that the Kspar and quartz has replaced
original plagioclase. If so, then this sample displays very
strong potassic alteration, later overprinted by phyllic alteration.
The ?potassic alteration is pervasive; the phyllic alteration
appears to increase towards one end of the slide, probably
near a later fracture.
Quartz forms irregular,
corroded-looking ?relict primary crystals up to 3 mm in diameter,
in places with what appear to be minor overgrowths at the
margins, and abundant finer-grained material in the matrix
of the rock that is clearly secondary in places (distributed
along narrow veinlets up to 1 mm thick, with strongly altered
margins).
Mafic sites are less
well-defined, consisting of irregular patches up to about
1 mm across of slightly coarser-grained (<0.3 mm) sericite
or muscovite, in places with chlorite up to 0.1 mm, and variable
amounts of sphene (subhedra to 0.4 mm, in places with included
minute rutile), or pyrite (euhedra mostly <0.35 mm in diameter).
Rare zircon forms euhedra to 40 microns diameter.
L00-13-219.70: PHYLLIC
(SERICITE-CHLORITE-CARBONATE-PYRITE-RUTILE) AND EARLY ?POTASSIC
(KSPAR-QUARTZ) ALTERED ?CRYSTAL TUFF OR INTRUSIVE
Hand sample is medium-grained
and massive, with an altered, vaguely porphyritic texture,
containing relict mafics cored by dark green chlorite and
rimmed by buff-brown ?ankerite. The rock is not magnetic and
shows no reaction to cold dilute HCl, but there is abundant
stain for K-feldspar in the etched slab. Modal mineralogy
in polished thin section is approximately:
|
K-feldspar (?largely secondary)
|
40%
|
|
Quartz (partly secondary)
|
20%
|
|
Sericite, clay
|
15%
|
|
Chlorite
|
15%
|
|
Carbonate (?dolomite or ankerite)
|
5%
|
|
Pyrite
|
1-2%
|
|
Rutile, sphene
|
1%
|
This slide is composed
of large subhedral crystals of simple Carlsbad twinned K-feldspar
up to 2.5 mm long, sericitized and chloritized ?mafic crystal
relics, and interstitial quartz.
The K-feldspar in places
reveal traces of relict twinned ?plagioclase within them,
suggesting that the Kspar has replaced formerly more extensive
plagioclase feldspar.
Quartz mostly forms subhedral
to irregular crystals that are optically continuous for up
to 1 mm and appear to be replacing or overgrowing surrounding
feldspar.
Sericite-carbonate-chlorite
altered relics have euhedral squarish outlines up to 2 mm
across; they may have been ?plagioclase or mafic crystals.
Chlorite-altered relics have irregular outlines up to 3.5
mm across, likely after former mafic minerals. Chlorite, forming
subhedral flakes mostly <0.15 mm in diameter, tends to
form the cores of the relics, with carbonate (and rutile)
at the rims. Carbonate, forming subhedra mostly <50 microns
in diameter, is likely dolomite or ankerite since it does
not appear to reaxt to HCl in hand specimen.
Pyrite forms coarse euhedral
cubic crystals up to 1 mm in diameter, locally aggregating
to several mm across. Rutile occurs as minute subhedra, possibly
with traces of sphene, commonly enclosed in carbonate.
It is difficult to tell,
given the level of alteration, but this sample appears to
have been a ?tuffaceous rock, perhaps a crystal tuff of mafic
to intermediate composition (although the texture is also
permissive of a porphyritic intrusive). It has undergone significant
?early potassic alteration to K-spar and quartz, overprinted
by later phyllic alteration to sericite, chlorite, pyrite,
dolomitic carbonate and rutile.
L00-13-221.50: INTENSE
PHYLLIC (QUARTZ STOCKWORKED, CLAY-SERICITE-CHLORITE- CARBONATE-RUTILE-SULFIDES)
AND ?EARLY KSPAR ALTERED IGNEOUS ROCK
Hand sample appears to
be a hydrothermal breccia, composed of angular, irregular,
vaguely defined blocks of rock in a matrix of quartz veins.
The included blocks of rock are greenish and buff-brown, similar
to the previous sample (219.70); significant pyrite is associated
with the quartz vein stockwork. Core areas of the blocks stain
yellow for K-feldspar in the etched slab, suggesting outer
rims of the blocks have been overprinted by silicification.
Modal mineralogy in polished thin section is approximately:
|
Quartz (largely secondary)
|
45%
|
|
Clay-sericite
|
25%
|
|
K-feldspar (?secondary)
|
10%
|
|
Chlorite
|
10%
|
|
Carbonate (?dolomite/ankerite)
|
5%
|
|
Pyrite
|
2-3%
|
|
Rutile
|
1-2%
|
|
Chalcopyrite
|
<1%
|
Remnants of wall rock
in this sample consist of rounded to irregular-shaped patches
of clay-sericite, chlorite, carbonate, and rutile with relics
of K-feldspar, all replaced by and separated by irregular
masses of quartz. The texture of the former rock is virtually
destroyed at the thin section scale. Former ?plagioclase crystals
appear to be completely replaced by clay-sericite (microscopic
flakes rarely over 15 microns in diameter), in places intimately
mixed with chlorite of similar size. Even K-feldspar crystals,
with subhedral outlines up to 1 mm across, are partly to mostly
replaced by clay-sericite. Former ?mafic crystals are pseudomorphed
by patches of chlorite (flakes up to 25 microns in diameter),
carbonate (likely dolomite or ankerite, subhedra to 25 microns),
and abundant rutile or leucoxene (anhedral patches up to 0.2
mm across composed of mostly amorphous material).
The intervening stocwork
areas are composed of anhedral to subhedral interlocking secondary
quartz crystals with minor clay-sericite, chlorite, sulfides
and rutile interstitial to the quartz. It is not possible
to be sure, but it appears that silicification and clay-sericite-chlorite-pyrite-rutile
alteration spread out from the quartz stockwork. (An alternative
would be that secondary quartz accompanied the K-feldspar
alteration, which appears to be earlier.)
Pyrite, forming large
subhedral crystals up to 2 mm across, and traces of chalcopyrite,
forming anhedral crystals mostly <0.2 mm across, are found
in both the quartz stockwork and the altered wall rock fragments;
chalcopyrite is closely associated with chlorite, and probably
represents replacement of former mafic minerals. Note that
minor amounts of chalcopyrite present as minute (<20 micron)
crystals encapsulated in quartz might not be liberated even
during fine grinding of the rock.
L00-13-224.20: INTENSE
PHYLLIC (QUARTZ STOCKWORKED, CLAY-SERICITE-CHLORITE- RUTILE-SULFIDES)
AND ?EARLY KSPAR ALTERED IGNEOUS ROCK
Hand sample is similar
to 221.50, consisting of angular, pale green altered fragments
in a quartz vein matrix or stocwork. Minor pyritic sulfides
are associated with the stockwork, and minor buff-coloured
?carbonate occurs with the chloritic fragments. The fragments
show abundant yellow stain for K-feldspar in the etched slab.
Modal mineralogy in polished thin section is approximately:
|
Quartz (mainly secondary)
|
50%
|
|
K-feldspar (?largely secondary)
|
25%
|
|
Clay-sericite
|
15%
|
|
Chlorite
|
5-7%
|
|
Pyrite
|
2-3%
|
|
Chalcopyrite
|
<1%
|
|
Rutile, leucoxene
|
<1%
|
|
Sphalerite
|
<1%
|
|
Galena
|
tr
|
Wallrock fragments are
mostly composed of large irregular-shaped patches, up to 2
mm across, of clay-sericite and lesser chlorite that appear
to be replacing feldspar (mostly K-feldspar to judge by the
extent of yellow stain in the etched slab). These patches
are intergrown with secondary quartz as sub- to anhedral crystals
up to 2.5 mm in diameter with ragged margins suggesting they
are overgrowing the adjacent minerals. Sericite flakes are
rarely up to 35 microns in diameter, mixed in places with
a very pale greenish or brownish chlorite of similar size.
Most chlorite, however, is bright green, forming flakes up
to almost 100 microns in diameter at the edges of chloritic
patches. Minor rutile is mixed with the chlorite as irregular
aggregates up to 0.5 mm across composed of almost amorphous
material (leucoxene).
The quartz stockwork
is composed of coarse subhedral crystals up to almost 0.5
cm in diameter. Minor amounts of clay-sericite and chlorite
are found along the boundaries between the crystals.
Sulfides, principally
coarse euhedral pyrite as cubes up to 4 mm across, tend to
line the margins of wall rock fragments at the contact with
quartz vein stockwork. The pyrite contains abundant inclusions
of silicates and rutile, and in places is associated with
traces of chalcopyrite, sphalerite and galena. Sphalerite
is associated with traces of galena and chalcopyrite, and
contains abundant submicroscopic inclusions of chalcopyrite
(see photomicrograph). Chalcopyrite is also found as minute
(<25 micron) blebs in the highly altered wallrock, especially
hosted in chlorite.
The original protolith
is not determinable due to the intense phyllic (quartz-clay-sericite-chlorite-
pyrite-rutile) and possibly earlier ?potassic (K-spar, quartz)
alteration.
L00-13-229.10: INTENSE
PHYLLIC (CLAY-SERICITE-CHLORITE-PYRITE-RUTILE) AND ?EARLY
KSPAR ALTERED/RARELY QUARTZ-KSPAR VEINED ?INTRUSIVE ROCK
Hand sample is a greenish
grey, massive, medium-grained, altered, pyritic ?intrusive
or tuffaceous rock cut by narrow white veins that stain yellow
for K-feldspar, as does much of the matrix of the rock. Modal
mineralogy in polished thin section is approximately:
|
Quartz (partly secondary)
|
30%
|
|
K-feldspar (?largely secondary)
|
25%
|
|
Clay-sericite
|
25%
|
|
Chlorite
|
15%
|
|
Pyrite
|
4-5%
|
|
Rutile
|
<1%
|
|
Chalcopyrite, trace ?galena
|
tr
|
This sample consists
of irregular-shaped patches of clay-sericite altered feldspar
(probably after both K-feldspar and plagioclase), subhedral
to irregular patches of chlorite and lesser clays-sericite
(after former mafics), all strongly overprinted by secondary
quartz that may have grown outwards from clumps of primary
quartz.
K-feldspar, indicated
by the yellow stain in the etched slab, is difficult to recognize
in thin section. It appears to form subhedral crystals up
to about 1 mm in diameter, that are mostly about half replaced
by clay-sericite and minor chlorite, with a lamellar texture
that may reflect primary plagioclase twinning. This suggests
that the K-feldspar may be largely secondary, having replaced
former plagioclase in an early potassic phase of alteration.
Some of the secondary quartz, which forms subhedral crystals
up to 2 mm across that poikilitically enclose other minerals
around their margins, may have formed at that time, but it
is difficult to be sure. The possibility of the K-spar being
secondary is supported by the presence of K-feldspar as euhedral
crystals up to 0.25 mm diameter, intergrown with quartz, along
narrow veinlets <1 mm thick.
Most of the clay-sericite
has negative relief compared to quartz and chlorite, but moderate
birefringence, suggesting that some or all of it could be
a montmorillonite- or smectite-group (swelling) clay. Individual
flakes are generally <20 microns in diameter.
Mafic relics are pseudomorphed
by chlorite as subhedral flakes mostly <25 microns in diameter,
in places with a rim of clay-sericite or mixed intimately
with clay-sericite. Clusters of rutile up to 0.2 mm across,
commonly asociated with the chloritized mafics, are composed
of euhedral dark brown crystals mostly <75 microns in size.
Pyrite occurs as cubic euhedra mostly <1 mm in diameter,
also commonly associated with the chloritized mafics. Rarely,
traces of chalcopyrite form subhedra to 0.15 mm associated
with the pyrite crystals, and traces of ?galena are included
in the pyrite crystals.
It is not clear what
the original protolith for this intensely phyllic (quartz-clay-sericite-chlorite-sulfides-rutile)
and possibly earlier potassic (Kspar-quartz) altered rock
was; it may have been a mafic-intermediate intrusive rock.
L00-13-231.05: INTENSE
PHYLLIC (?QUARTZ, CLAY-SERICITE-CHLORITE-PYRITE-RUTILE) AND
?EARLY KSPAR-QUARTZ ALTERED ?INTRUSIVE ROCK
Hand sample is a medium
grained, greenish, mottled (strongly altered) ?igneous rock
of intermediate to mafic composition, cut by veins up to 0.7
cm thick containing massive pyrite. Minor stain for K-feldspar
in the etched slab suggests that K-spar is in part controlled
by the veins and therefore is secondary. Modal mineralogy
in polished thin section is approximately:
|
Quartz (largely secondary)
|
35%
|
|
Chlorite
|
25%
|
|
Clay-sericite
|
25%
|
|
K-feldspar (partly secondary)
|
10%
|
|
Pyrite
|
5%
|
|
Rutile
|
<1%
|
|
Sphalerite
|
<1%
|
|
Chalcopyrite
|
tr
|
This sample is similar
to the previous six or seven samples, with intense alteration
obscuring primary lithology of a fine-grained ?intrusive rock.
Irregular-shaped patches of clay-sericite or chlorite and
pyrite+rutile, or mixtures of chlorite and clay-sericite,
are embedded in a matrix of quartz (possibly largely secondary),
K-feldspar and chlorite. It is possible that the larger patches,
about 2 mm in diameter, represent former phenocrysts of either
mafic or feldspar crystals (or both) but this is not certain
since the texture could be merely due to alteration.
K-feldspar is difficult
to recognize in thin section due probably to strong replacement
by clay-sericite, which forms minute (5 micron) to fine-grained
(25 micron) flakes. The shapes of former feldspar crystals
are obscured by strong replacement around the margins by secondary
quartz. The quartz crystals commonly have subhedral outlines
that are optically continuous for up to 1 mm, poikilitically
enclosing altered feldspar remnants or chloritized mafic relics.
It is not clear how much, if any, of the quartz may have been
primary.
Chlorite forms pale green
flakes up to 75 microns in diameter, commonly containing or
associated with pyrite and rutile. Yellowish-brown rutile
forms euhedral crystals up to 0.1 mm diameter, in places aggregating
to 0.25 mm.
Narrow irregular discontinuous
quartz veinlets up to 0.1 mm thick cross the rock. The major
vein is composed of pyrite, with quartz and chlorite selvages,
and appears to have a concentration of K-feldspar in envelopes
along one side of the vein, and clay-sericite-chlorite on
the other side.
Pyrite, forming euhedral
crystals up to several mm across in massive aggregates in
the major vein, or millimeter-sized crystals in the wallrock,
is rarely associated with or contains rounded inclusions of
sphalerite up to 0.75 mm across. The sphalerite is colourless
(Fe-poor) but contains abundant round blebs of chalcopyrite
<10 microns in diameter.
L00-13-241.30: PHYLLIC
(CLAY-SERICITE-CHLORITE-?QUARTZ-PYRITE-RUTILE) AND ?EARLY
KSPAR ALTERED IGNEOUS ROCK CUT BY QUARTZ-CHLORITE-PYRITE-
CHALCOPYRITE ZONE
Hand sample is greenish-grey
and strongly altered, with a mottled to disrupted appearance,
cut by irregular zones with pyrite and chalcopyrite that are
associated with stronger chloritization. There is extensive
pale yellow stain for K-feldspar in the etched slab, likely
pale coloured due to clay-sericite alteration of the feldspar.
Modal mineralogy in polished thin section is approximately:
|
Quartz (?largely secondary)
|
40%
|
|
Clay-sericite
|
35%
|
|
Chlorite
|
10%
|
|
K-feldspar (relict, ?secondary)
|
10%
|
|
Pyrite
|
3-5%
|
|
Chalcopyrite
|
<1%
|
|
Rutile
|
<1%
|
|
Apatite, ?zircon
|
tr
|
The major altered zone
(not a vein) is composed of coarse-grained subhedal pyrite
(aggregates up to 4 mm across) with associated chalcopyrite
(subhedra to 1.2 mm) in a matrix of secondary quartz (subhedra
to 2.5 mm diameter) and chlorite (bright green rosettes up
to 0.25 mm in diameter) plus lesser clay-sericite. In places
the clay-sericite has a radial rosette-like habit that is
similar to pyrophyllite (characteristic of a highly aluminous
assemblage, but it cannot be identifed with certainty except
by microchemical tests such as scanning electron microscope,
or SEM).
Away from the major altered
zone, the wallrock consists mainly of relict patches of strongly
clay-sericite altered feldspar (partly K-feldspar to judge
by the yellow stain in the etched slab) and chlorite-rutile
altered mafic relics, both intensely overprinted by secondary
quartz. Some or most of the K-feldspar may be secondary; it
appears to predate the phyllic (clay-sericite) alteration.
Note that the quartz overprint may have accompanied the early
|