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Two Noteworthy Occurrences Exposed During Highway Construction, Hull Township

Last Updated: 15th Mar 2013

By Phil M. Belley

I wrote this short article from January to February 2009 and presented it at the Rochester
Mineralogical Symposium in April 2009. The coauthors for the RMS presentation are Ralph Rowe
and Michel Picard, who both offered well-needed help with many aspects of the project. A big
thanks to them and to everyone else involved with this project; see 'Acknowledgments'.




Location


This locality is situated 25 km NNW of Ottawa, Ontario, in the north of Hull Township,
Gatineau County, Quebec. Contiguous to the eastern edge of Gatineau National Park, it is
located in beautiful uplands full of lakes, thick forests, and abandoned mines.

01227360014949811007383.jpg
Extension Map


Introduction


During extensive blasting and excavation for the construction of a Highway-5 extension,
which took place throughout 2008, I was able to study the newly exposed formations and recover
a considerable variety of mineral species including many samples remarkable for the quantity,
quality or size of the crystals. The highlight was certainly a series of slightly inclined vertical
solid calcite veins in igneous rock hosting well formed crystals of schorl and altered ilmenite, as
well as numerous other silicates, phosphates, sulfides, and oxides. In late summer 2008, blasting
exposed a sulfide-and-silicate-rich solid calcite vein cutting metasediments in the southern area
of the extension. Fantastic specimens of molybdenite were recovered from the lower wall and
floor of this road-cut. The geology at the new road segment is rich in various suites of
metamorphic and igneous rocks and bears resemblance to the geology of two nearby brucite
quarries, the Stephen Cross and Maxwell.

A note on specimen preparation: Calcite has often been removed from specimens using hydrochloric acid. This method was used often with Schorl-Ilmenite Occurrence material, and less frequently with Molybdenite Occurrence material. Several specimens from both localities were treated with ethanoic/acetic acid (5%) instead.

Schorl & Ilmenite Occurrence


Two principal veins, subparallel to the new road, were observed; one on the floor of the roadcut,
the other on the wall. Other veins were possibly encountered during construction and hidden
under piles of crushed stone. One vein was calcite filled and up to 20 cm wide. The other was a
vein remnant on the wall of the road-cut, mud-filled as a result of calcite weathering.

04453730014948843109283.jpg
Part of a schorl vein on the east cut of the east lane, Highway-5. Larger sections of the vein were at this point removed for specimen recovery. May 2008.
01844460014949811002734.jpg
Schorl crystals, to approx. 2 cm, in a mud-filled vein on the wall of the east cut, east lane, Highway 5. May 2008.



Mineralogical Assemblage


Anatase

Anatase partly replaces crystals of ilmenite and is most frequently mixed with rutile and
hematite. Some pseudomorphs have irregular zones of brownish-yellow “leucoxene”, a mixture
of rutile and anatase. Occasionally, crystals are covered with leucoxene as well.

Apatite
A relatively common mineral in the veins, and abundant in localized areas, apatite is found as
colorless and yellowish transparent prismatic crystals to 3 mm in length. Both basal and complex
terminations have been observed. It is probably the fluorine analogue of this mineral based on
the widespread occurrence of fluorapatite throughout the region.

Brookite
Brookite occurs rarely as a replacement of ilmenite. It is associated with rutile, hematite, anatase
and titanite.

Calcite
White to grayish calcite occurs as anhedral crystals to over 3 cm and is the principal vein
constituent.

Clinochlore
Occurs as a greenish-gray replacement of mica. Small mica crystals are frequently altered
completely to clinochlore while larger crystals are altered only on the exterior.

02319900014949811027001.jpg
Clinochlore ps. Mica, 1 mm crystals.


Feldspar Group
Feldspar crystals are common as colorless, transparent and lustrous micro-crystals covering the
host rock. They are associated with apatite micro-crystals. In other areas they can be found as
larger translucent crystals, to 23 mm, having a pale pink tint. In the main vein, the specimens
with larger crystals show a different paragenesis, in which the feldspar formed after the mica. It
is yet undetermined if both habits are the same species.

07123810014949811026731.jpg
Feldspar crystals to 12 mm.


Fluorite
Fluorite is a rare late-stage vein material and occurs as pale to emerald green subhedral crystals.

Hematite
Hematite replaces, in part, crystals of ilmenite. It is associated with rutile, anatase, brookite, and
titanite.

Ilmenite
Well-formed crystals of ilmenite to 32 mm have been recovered from the site, commonly
replaced by different combinations of rutile, anatase, brookite, hematite and titanite. The
pseudomorphs, frequently dull, can be opaque pale grayish, pinkish-gray and pastel
yellow in color. Unaltered crystals tend to be smaller, to 12 mm, and are dark gray to black.
Ilmenite is a fairly common vein material.

07549690014949811022007.jpg
Left: unaltered ilmenite crystals to 13 mm, center: altered crystals to grey mixture (hematite, rutile, anatase), lower mid-right: see close-up


06919840014948843903757.jpg
Close-up. Crystals to about 4mm of altered ilmenite. Tan-coloured material is mostly anatase+rutile.


Magnetite
Magnetite is found as small, euhedral, and lustrous octahedrons to approximately 2 mm alone or
on ilmenite.

Mica Group
A Mica-Group mineral occurs at the locality as crystals to 3 cm and parallel aggregates, often
replaced by chlorite. The mica, when unchanged, is of a dark amber color. Many localized areas
within the deposit are enriched with mica, while other zones are devoid of it.

Molybdenite
Only one specimen of molybdenite was recovered at the locality and consists of a single
bluish-gray hexagonal crystal under 1 cm on matrix.

Monazite
Uncommon, orange to brown euhedral monazite crystals, seldom more than 2 mm in size, have been
found in both veins.

Pyrite
Pyrite is a late stage mineral and is found as irregular bright golden crystals to 1 cm. It is
uncommon in the main veins.

Pyrrhotite
Pyrrhotite is found rarely as rounded yellowish-brown masses associated with pyrite. They
usually display tiny parallel crystal faces.

Quartz
Rounded crystals of gray quartz to 4 cm are very common throughout the occurrence. They
exhibit abundant parallel growth and are associated with most minerals. Rarely, massive quartz
will fill parts of the vein and will enclose schorl crystals, some which are over 4 cm.

09781140014949811026901.jpg
Altered ilmenite crystals to 8 mm on quartz crystals, with clinochlore ps. after mica.


Rutile
Rutile is found as an alteration of ilmenite, usually intermixed with anatase, hematite, and other
titanium minerals. In the vein found on the wall, small ilmenite crystals are completely altered to
euhedral brownish-red rutile crystals (< 3 mm) and clusters, some twinned. Rarely, the entire
shape of the ilmenite will be preserved in specimens from this vein.

08073640014948843767281.jpg
Ilmenite crystal (3 mm) completely replaced by tiny rutile crystals.


Schorl
Short-prismatic, black euhedral crystals of titanium-bearing schorl, have been found at the locality. They
are lustrous, devoid of striations, and reach a length of 55 mm. They are very similar in
appearance to tourmalines from Power’s Farm (Pierrepont, NY, USA) and Tait Farm
(Dungannon tp., Ontario, CA). Some crystals were subject to in-solution breakage and have
subsequently re-crystallized.

00373800014947784685210.jpg
Schorl crystals to 2 cm with altered ilmenite crystals to 13 mm.


Titanite
Sub-millimeter wedge-shaped reddish-brown crystals of titanite can be found as a rare accessory
mineral. Also replaces ilmenite, in rare cases.


Molybdenite Occurrence


Several calcite veins were exposed on the wall and floor of the west cut on the northbound
road. The smaller veins, all less than 8 cm wide, are pyroxene-rich. The larger vein, 20 cm wide
at most and having a NE-SW orientation, has produced the best and largest crystals of
molybdenite found at the highway-5 extension.

04029580014948842477317.jpg
Main molybdenite-bearing vein (blue arrow) and smaller vein (green arrow). September 2008.
01208020014949811035558.jpg
Main molybdenite-bearing vein exposed on the floor of the road cut. This was excavated for specimen recovery. September 2008.
07254490014948841524140.jpg
Molybdenite crystals in the main calcite vein exposed at the bottom of the small excavation. September 2008.


Mineralogical Assemblage

Amphibole Group
Dark green to black crystals under 5 cm and intergrown masses are common in the main vein.

Apatite
Pastel-yellow prismatic crystals to approximately 8 mm are associated with pyroxene.
They are commonly found in the smaller veins.

07476580014948844587624.jpg
Rounded 4 mm apatite on white feldspar and forest-green pyroxene. From a small vein.


Calcite
In the main vein, calcite is yellowish to gray and white. It fluoresces pinkish-red when exposed
to short-wave ultraviolet radiation. In the other veins, calcite has a yellow-green
coloration due to chlorite inclusions.

Chlorite Group
Microscopic crystals are included in the calcite, giving it a yellow-green color. This has only
been observed in the small veins.

Feldspar Group
Grayish-white feldspar crystals are common throughout the area. The larger crystals, up to 2 cm
in diameter, are found in the largest vein.

Mica Group
The principal vein contains abundant microscopic dark brown crystals and crystals up to 3 cm on
occasion.

Molybdenite
Superb metallic bluish-gray molybdenite crystals to 6 cm in diameter were collected from the
larger vein. Crystals to 13 mm were found in one of the green calcite veins.
Parallel growth and bent crystals are common.

02069380014949811045487.jpg
38 mm crystal on matrix. From main vein.


04170650014948841374432.jpg
6 cm specimen. From main vein.


Pyrite
Pyrite is relatively common as golden-yellow euhedral micro-crystals and possibly as partly
altered masses. No iron sulfides were observed in the smaller veins.

Pyroxene Group
Forest-green, translucent pyroxene crystals to over 2.3 cm line the contact between the
host rock and green calcite.

01369030014948841548968.jpg
Pyroxene crystals with molybdenite to ~15 mm. From a small vein.


Pyrrhotite
Yellow brown pyrrhotite crystals to just over 2 mm and ‘etched’ masses in excess of 15
cm commonly occur in the larger vein.

07514410014948842115506.jpg
Pyrrhotite crystals to 2 mm with amphibole. From main vein.


Quartz
Lightly to heavily rounded quartz and smoky quartz crystals up to 5 cm occur in all the veins.

Titanite
Reddish-brown wedge-shaped crystals to 3 mm occur sparingly. The diaphaneity is transparent,
but they usually appear opaque due to internal fractures and inclusions.

Possible Origin of these Hydrothermal Deposits


Situated in the Central Metasedimentary Belt of the Grenville Province, the highway-5
extension is built over part of the Wakefield batholith – a large Precambrian intrusive composed
of syenite and monzonite, which can contain from 5% to 15% magnetite and titanite (Béland,
p.40), and has been subjected to slight metamorphism. A generalized bedrock geology map of
the area (GSC map 1508A, 1980) reveals that this intrusive is the principal constituent of the
bedrock at the locality. At a distance, large bodies of metamorphic rocks (i.e.: marble, skarn,
gneiss) and igneous rocks (i.e.: diorite, gabbro, anorthosite) are present. Smaller, but still
significant exposures of various metamorphic rocks were observed in the field, notably marble,
calc-silicate rocks and serpentine-rich rocks.
Solid calcite veins of hydrothermal origin are common throughout the area and fill fractures
in both plutonic and metamorphic rocks. They frequently swell and pinch. All of these veins,
except in rare cases, contain considerable quantities of quartz, pyrite, fluorite and/or
molybdenite. The mineralogy clearly reflects the reactions between country rock and fluids: for
example, the syenite/monzonite contains important quantities of titanium; the schorl-ilmenite
vein is rich in titanium-bearing minerals. Similar hydrothermal deposits are abundant in all rock types at
the locality, suggesting that they formed from a widespread geologic feature. Similarities in Fe,
Mo, S, F abundances in the deposits support this theory. This feature is the contacts of the
Wakefield batholith with Grenville series rocks – hydrothermal deposits are always intimately
associated with them, whether directly between both or filling fractures in either.

Conclusion


The unique mineral specimens discovered at the highway-5 extension are evidence of the
interesting geological history of the area. Many rock types contained fractures, which were
filled by hydrothermal fluids originating from the crystallizing syenite/monzonite. The construction
project offered local collectors an incredible opportunity to collect very unique and beautiful
samples. Most importantly, fascinating specimens were recovered for museums.

Acknowledgments


I wish to thank Ralph Rowe and Michel Picard for field assistance and providing information from
their own fieldwork, Mr. Rowe and Glenn Poirier for generously taking the time for specimen analysis
so I could have the required data for my presentation, Michel Belley for providing well-needed
assistance in field and chemical work. I would also like to thank Daniel Russell, Sophia Schultz, Paul
& Nathalie Brandes, Roger Lang, Stephen Callaghan, and Nicole Caverly for reviewing my article and
offering useful suggestions. For my presentation, I thank Michael Bainbridge for the fantastic photographs
he provided - they made my presentation much more impressive - and André Lalonde for making my talk at RMS
possible!


Bibliography



Béland, René. Exploration Géologique: Région de Wakefield. Québec: Ministère des Richesses
Naturelles, 1977.

Hogarth, D.D., et al. Classic Mineral Collecting Localities in Ontario and Quebec. Ottawa:
Geological Survey of Canada, 1983.

Hogarth, D.D. Geology of the southern part of Gatineau Park, National Capital Region. Ottawa:
Dept. of Energy, Mines and Resources, 1970.

Lentz, David Richard. U-, Mo-, and REE-bearing pegmatites, skarns and veins in the central
metasedimentary belt, Grenville Province, Ontario
. Sudbury, ON: Geological Association of
Canada, 1991.


Updates


2009 - April - 28 - Article posted
2009 - May - 1 - Minor photo formatting corrections and specimen photo embeds.
2009 - May - 8 - Several photos added. Note on specimen prep added.












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