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Snee Hall Rock Park Details

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1 Hyaloclastite, or "pillow breccia"

Composition: basaltic, consisting of very small crystals of feldspars, amphiboles, pyroxenes, olivine, and crystallized glass of the same bulk composition, with chlorite, epidote, carbonate, and quarz as alteration products.  Source: Ramore, Ontario.

Hyaloclastites form near submarine volcanic vents.  Rapid chilling of the basaltic lava causes it to form glass (obsidian) at its outer margins while the interior parts cool more slowly to become fine-grained basalt.   The chilled marggins can be seen as lighter-colored rinds around the larger clasts.  Lobed structues, called pillows because of their resemblance to a pile of pillows, form when the lava flows away from the vent.  The hyaloclastite breccia was formed from the debris of pillows that were shattered by their rapid cooling.


Rock22 "Drop stone" tillite: Coleman member, Gowganda Formation

Composition: bedded wackestone with large granitic clasts. Cource: Coniagas pit, Agnico-Eagle Mines, Cobalt, Ontario. The dark gray matrix of this rock formed as clay, silt, and sand were deposited in a lake or bay in front of a glacier. As icebergs that calved from the glacier melted, they dropped larger rocks into the sediment. If you look closely around the rim of the large granitic clast, you can see where sediment layers were deformed by the impact of the rock and where later sediments were draped over it. From those features you can deduce which direction was up when the sediments were deposited.


Rock33 Tillite: Gowganda Formation

Composition: an assortment of rounded pebbles, cobbles, and boulders formed of granite (red-orange), mudstone (medium green), meta-diorite (pale green and mottled), and basalt (dark green), in a poorly sorted matrix of clay, silt, and sand. Source: Kenogami, Ontario. Tillites are rocks formed by the lithification (conversion to rock) of one of the types of sediments left behind by glaciers. Thus this rock may be evidence of an ice age during the early Proterozoic Era. Recent deposits of such glacial sediments, not yet lithified, may be seen in the Ithaca area, where streams have cut down through moraines left during the most recent ice age, which ended about 12,000 years ago.


 Rock44 Folded gneiss: Metachewan gneiss (informal)

Composition: pink and white bands -- mostly orthoclase (pink feldspar) and plagioclase (white feldspar) with minor quartz; dark gray bands -- mostly biotite and quartz.  Source: seven miles west of Kenogami Lake, Ontario. Bneisses are produced by the metamorphism of ordinary rocks, such as granites of shales. Burial dep in the earth's crust subjected these rocks to sufficient heat and pressure to cause new minerals to grow and become arranged in light and dark bands. The rocks are changed so much from their original apperance that often we may only guess at their origin from their compostion. This specimen was also subjected to compressional forces, perhaps at a later time, that folded the gneissic banding.

Rock55 & 6 Onaping tuff, or breccia: Grey member, Onaping Formation, Whitewater Group

Composition: dust-to boulder-sized fragments of shattered rock, including, quartzite and granite with blobs and fragments of recrystallized glass. Source: Sudbury Structure, Onaping Falls, Ontario. A tuff is a deposit of the debris from volcanic explosions such as the one at Mount Saint Helens in 1980. It consists of shattered hot rock and lava. Many geologists believe that the Onaping tuff is an exceptional nonvolcanic one. It might be a "fallback breccia" that formed when a large meteorite struck the Sudbury area 1.85 billion years ago, pulverizing a large quantity of the metamorphic and igneous rocks at the impact site. You can see a large (20 cm) blob of recrystallized glass in the smaller of the two rocks. It is somewhat tanner in color then the rest of the rock and is more easity seen when wet. The glass was formed when the rocks were melted by the heat generated by the impact. In thin sections under the microscope you can see that some of the mineral grains were deformed by an intense shock wave and some clasts have glassy rims, indicating that a violent event occurred. Many features of the Sudbury structure are not explained by the impact ehory, so the question of its origin is not yet resolved. See #7 below.

 Rock77 Shatter cone: Mississagi Formation

Compositions: arkosic wacke, a gine-grained sedimentary rock; however, what is of interest is the conical fracturing, most evident near the top of the specimen. Source: Sudbury, Ontario, near Hannah Lake. Shatter cone fractures are usually associated with known and suspected meteorite impact scars (astroblemes). None is know to have formed by nonmeteoritic geolgic processes. The shock wave produced by the impact sent fractures propagating through the rocks surrounding the impact crater through the rocks surrounding the impact crater (the Sudbury basin). Where they intersected irregularities in the rocks, conelike fractures such as this one are found pointing toward the impact site. The presence of shatter cones in many of the rocks surrounding the Sudbury basin supports the impact theory of its origin.

 Rock98 & 9 "Virginite" gold ore

Composition: white and pink (iron-stained) quartz veins with plagioclase (tan due to staining); pink syenite veins that intruded into metasomatically altered host rocks (Timiskaming metasediments) and were made green due to fuchsite or purplish gray due to stained biotite and sericite; also pyrite and gold. Source: McBean Mine, Colby, Ontario, along the Larder Lake "Break." 

Specimen 8 is from the contact zone between an intrusive igneous rock, the pink syenite, and the green rock that it intruded. The heat, volatiles, and trace elements released by the syenite as it cooled altered the composition of the surrounding rocks. That kind of alteration is called metasomatism. In this case one of the new minerals to be formed was fuchsite, a mineral similar to ordinary mica except that it contains chromium, which gives the fuchsite its green color. Another mineral introduced to the country rock was gold, in sufficient quantities to form a minable ore deposit. What looks like gold in this specimen is actually pryite. The real gold is so sparse that it is unlikely you will see any. In fact this entire rock probably contains less than 0.01 oz of gold, yet it is ore grade. Specimen 9 was found farther from the intrusive contact and thus lacks the bands of syenite. This rock is sometimes mined as gold ore at the McBean mine; however, most of the gold ore occurs in the outer parts of the syenite and in the contact zone. 

The green fuchsite is often a clue to prospectors that a gold deposit is nearby. It has been used as an exploration guide in many places, including Canada and the Mother Lode region of California, originated on the Baie Verte Peninsula of Newfoundland during the 1950's. There similarly spectacular green rocks are exposed for 60km of strike.

 Rock1010 Magnetic banded iron formation

Composition: magnetite (black, fine-grained), biotite (black, course-grained, to 1 cm), orthoclase (pink to white, very coarse grained, some as porphyroblasts, some in intrusive veins), amphibole (dark green, acicular), and pyrite. The matrix (gray material between magnetite bands) is mostly chert with minor sericite. Source: Adams Mine, near Kirkland Lake, Ontario.

Branded iron formation is a common iron ore and is usually extracted from huge open-pit mines such as Adams Mine. This ore formed as a chemical precipitate during the Archean Era, about 2.7 billion years ago. One likely hypothesis is that dissolved iron was carried from the land surface by rivers and from undersea hot springs by currents to restricted basins where oxygen, probably produced by the earlies photosynthetic algae, was available to convert the iron into insoluble iron oxides. The iron oxides and chert precipitated onto the shallow seafloor, forming a deposit that , in the case, was buried and metamorphosed.

One side of this rock is smooth and rounded with gentle grooves on its surface. The striations were formed by glacial abrasion during the last ice age. Also note that the bedding has been folded and offset along a fault

 Rock1111 Jaspilitic banded iron formation

Composition: magnetite (silvery gray), jasper (crypto-crystalline quartz, red in color owing to hematite), and pyrite (drusy fracture filling, i.e., fine-grained coating along fractures). Source: Sherman Mine, Temagami, Ontario.

Jaspilitic banded iron formation is also mined as iron ore. Hematite, the mineral responsible for its red color, is a form of iron oxide that contains more oxygen than magnetite and is not very magnetic, although there is enough magnetite in this specimen and in #10 to attract a magnet.  The deposit consists of two parallel bands of ore located a mile apart. Each is well over a mile long within an iron formation over six miles long. The ore contains 25-30 percent iron. It is crushed, and the hematite is concentrated to form pellets containing about 67 percent iron, which were shipped by rail to Hamilton, Ontario to be smelted into iron.

On one end of this specimen is contact with basalt, possible an intrusive dike.


Rock1212 "Stringer ore"

Composition: quartz, pyrite (pale yellow), chalcopyrite (brassy yellow), sphalerite (brown, rusty-looking owing to weathering), and siliceous gray rhyolite host rock. Source: Kidd Creek Mine, Timmins, Ontario.

There are four ore specimens in this park from the world-famous Kidd Creek Mine (specimens 12, 13, 14, and 15). The ore body is the largest known volcanogenic massive sulphide ore deposit, often referred to as the Kuroko-type, named after the excellent examples in northwestern Honshu, Japan. Originally the Kidd Creek ore body contained at least 150 million tons of ore, with typical grades of 1.5 percent copper, 9.7 percent zinc, 0.4 percent lead, and 4.3 oz silver per ton. Half of the ore has now been mined. It is not yet known how deep the ore extends.

The mine produces primarily copper and zinc from chalcopyrite and sphalerite. The specimens in the park represent the different types of ore present in the deposit, and each illustrates a different kind of environment in which the ore minerals were deposited.

A Kuroko-type deposit is one that formed on or adjacent to an undersea volcano during periods of quiescence in an episode of rhyolitic volcanism. The heat of the magma deep inside the volcano created a convective flow of the pore waters through a large volume of the surrounding rock. As the heated waters passed through the rock, they dissolved trace elements, such as copper and zinc, and then rose buoyantly to be dischared at a seafloor hydrothermal vent. When the hot mineral-laden water encountered cold seawater, much of its mineral load was immediately precipitated in the vicinity of the vent.

Stringer ores were precipitated in the relatively cool rocks a few tens of meters below the rock-seawater interface, where the water cooled slightly before it was discharged. Quartz and chalcopyrite were deposited in cracks and as replacement minerals in pipelike bodies just below the vent.

Rock1313 Massive and banded chalcopyrite ore

Composition: chalcopyrite, pyrite, sphalerite (brown), and quartz and sericite matrix (dark gray). Source: Kidd Creek Mine, Immmins, Ontario.

See #12, above. This is an example of high-grade copper-zinc ore. It was chemically precipitated at the mouth of a submarine thermal spring, where hot sulfide- and metal-rich waters came into contact with cold seawater. Pyrite, chalcopyrite, and sphalerite piled up around the vent or vents on top of the stringer ore (#12). This kind of ore is actually a sedimentary rock and is typical of Kuroko-type deposits.

Rock1414 Breccia ore

Composition: carbonaceous argillite (black), pyrite (pale yellow, medium brown, and rusty in places owing to weathering), sphalerite (reddish brown, rusty-looking streaks), and chalcopyrite (brassy yellow, associated with sphalerite). Source: Kidd Creek Mine, Timmins, Ontario.

See #12 and #13 above. The deposits of sulfide minerals that piled up around the hydrothermal vents on the flanks of the undersea volcanoes were sometimes situated on steep slopes. Breccia ores formed when those piles collapsed, slid down the slope, and were smashed into rubble and mixed with ordinary sediment. Thus this ore may be found some distance away from the source vent.

 Rock1515 Sulphide laminae in argillite with breccia ore

Composition: carbonaceous argillite (black) and pyrite (pale yellow, medium brown, and rusty in places owing to weathering). No ore minerals are readily visible. Source: Kidd Creek Mine, Timmins, Ontario.

See #12, #13, and #14, above. The hot water that left the vent after dumping part of its metal load rose as a plume until it cooled enough to become denser than the surrounding seawater. It then sank anc collected in local basins on the seafloor. Minerals continued to precipitate as it cooled and reacted with the seawater and sediments. When that occurred far enough away from the vent for the ore minerals to be diluted with ordinary sediments - mud, silt, and organic matter, for example - argillite and sulphide laminae were deposited.

"Ore" is an economic term that implies that a sufficient quantity of rock contains a large enough percentage of some valuable mineral to be profitable mined. Although this rock may contain some potentially valuable minerals and is part of an ore deposit, it may no be of high enough grade to be properly called ore.

Rock1616 Argillic siltstone, Firstbrook member, Gowganda Formation.

Composition: clay, silt, with chlorite (dark green crystals) from metamorphic alteration. Source: Cobalt, Ontario.

Note the angular internal slump folds (wavy bedding). The folds are evidence that this rock formed as a sedimentary deposit on a gentle slope. Gravity caused the beds of mud and silt to slide downhill, breaking and folding the beds before the sediment was hardened into rock.



17 18 19 Meta-syenit and mylonite

Composition: plagioclase (white, pale gray), amphibole (dark green) partly altered to chlorite, orthoclase (pink), and quartz. Source: Parry Sound, Ontario.

A mylonite is a rock that has been so intensely sheared by movement along a fault that the entire rock shows flow structure, rather than discrete fractures. Specimen 17 is an example of underformed rock from this locality. Note the large amphibole and plagioclase crystals and lack of any lineation. Specimen 19 is a rock of bulk composition similar to specimen 16, but it has been intensely sheared. The shearing caused the lineations and banding in #18 and #19 that appear as alignments of mineral grains.

Specimen 18 shows a special feature that can also be seen in specimen 19, though not as well. Large crystals of plagioclase with pink orthoclase rims escaped strong, deformation as the rock around them sheared freely, but they were rotated as the matrix flowed around them. The sense of rotation may be discerned by the orientation of the small "tails" of orthoclase that extend into the martix.

 Rock2020 Zinc ore

Composition: sphalerite (dark brown), pyrite, and serpentine (green fracture fillings). Source: Balmat Mine, Bouverneur, New York.

This specimen is from one of the largest zinc mines in the United States. Compare the the much coarser size of the sphalerite grains in this rock with those in #13. Recrystallization during the Grenville metamorphic event caused that. The large grain size is a potential advantage in the milling of such ores because they need not be ground so finely as other in order to separate all the ore minerals from the gangue (minterals not economically desireable). On first inspection it may appear that this specimen contains a fair amount of gangue. If you look more closely, you will see that the gangue is actually thin fracture fillings and constitutes a small percentage of the rock.


Rock2121 Stromatolites

Composition: marble (tan, calcite), tremolite (white needles), and talc (gray). Source: Gouverneur, New York.

Note the large lenslink structures in this specimen. They are trace fossils called stromatolites. They were formed by mats of algae or bacteria that trapped sediment particles on shallow seafloors, creating small mounds with the convex surfaces on top, and are indirect evidence of life in the late Proterozoic Era, over 1.2 billion years ago, when the Grenville Supergroup sediments were deposited. This rock was deliberately placed so the stromatolites are upside down (the convex sides of the stromatolites are on the bottom) because that was how the rock was found in place at the outcrop. The rocks had been overturned by mountain-building processes. Recognition of these stromatolites provided the first direct proof of the original order of succession of the metamorphosed Grenville sediments.

Rock2222 Mafic roof pendant

Composition: hornblende and chlorite pseudomorphs after pyroxene, and intrusive granodiorite (minor). Source: Route 11 near Round Lake, Ontario.

This may originally have been a mafic volcanic rock that was subjected to proxene-facies-contact metamorphism, which formed large crystals of pyroxene, and then retrograded to hornblende. It was subsequently metamorphosed by the Round Lake Granodiorite intrusion, which partly altered the hornblende chlorite. Small intrusive veins of the granodiorite outline crystals are in the lower right corner.

 Rock2323 Variolitic lava: Blake River Volcanics, Cadillac Group

Composition: intermediate in bulk composition, yet separated into more basic (darker colored matrix) and felsic (lighter-colored variolites) fractions. Source: Rouyn, Quebec.

One explanation for the presence of variolitic lavas is that they are the products of magmas caught in the act of separating into two quite different magmas. Like a mixture of oil and water, the mafic (iron- and magnesium-rick, silica-poor, like basalt) and felsic (sodium-, potassium-, aluminum-, and silica-rich, like rhyolite) components of the magma formed two immiscible liquids that were just beginning to separate when the magma erupted onto the surface and cooled.

Another explanation is that two different magmas, one felsic, one mafic, were stirred together but did not mix.

Rock2424 Jaspilitic banded iron formation

Composition: hematite, quartz, and magnetite. Source: Sherman Mine, Temagami, Ontario.

See #11 above.






Rock2625 26 27 Shawmere anorthosite

Composition: recrystallized plagioclase (whitish), amphibole (dark green, partly or wholly altered to chlorite), garnet (red), epidote (yellow-green), and orthoclase (pink). Source: Foleyet, Ontario.

Anorthosites are coarse-grained felsic igneous rocks that formed from magmas cooled slowly deep in the earth's crust. Because of their lower density, the plagioclase crystals floated upward and accumulated near the roof of the molten region and formed a rock that was almost entirely plagioclase.

An interesting feature of these specimens is that the originally large plagioclase crystals have been greatly elongated and recrystallized in a much finer grain size. However, the original large-grain outlines can still be seen on one surface.

Many boulders of anorthosite in the Ithaca area were transported here from the Adirondacks by the glaciers of the last ice age.

Rock2828 Garnetiferous diorite

Compositoin: almandite-pyrope garnet, plagioclase, and hornblende. Source: Barton Mine, Gore Mountain, in the eastern Adirondacks near North Creek, New York.

This specimen came from one ot the few localities in the world where huge garnets, some over two feet in diameter, are common. The garnets were formed along the contact of a gabbro and a syenite during the Grenville metamorphic event about a billion years ago. The very large crystal on the one end has a rim of hornblende that formed from the rock constituents not incorporated in the growing garnet.

The garnet mines of this region produce most of the world's supply of garnet for sandpaper and other abrasives.


dawn_redwoodMetasequoia glyptostrovoides, 

a "living fossil". It's common name is dawn redwood. This deciduous tree is differnt from the California redwood. It characteristics are closest to the cypress tree. Until it was discovered growing in northern China in 1940, it was thought to have been extinct since the Miocene.