|- Red Hills|
The Red Hill Range
The Red Hills are the most colourful and geologically interesting range in New Zealand and one of the more unusual world wide. They are mainly formed of a peridotite or dunite named after "Dun Mountain" a member of the same group found in Nelson three hundred miles to the north. The southern sector lies about 25 miles west of Mt Aspiring, on the western side of the Alps.
A dunite consists mainly of the mineral olivine (Mg,Fe)SiO4) with accessory chromite and spinel. Sometimes harzburgite containing minor orthopyroxne and a little gabbro and anorthosite may be found. Because of the high iron content, the hills weather a deep red, brown and orange from the limonite formed. Being deficient in Ca, Na, K, P, Bo and other essential minerals, no vegetation grows on them, but they are not "toxic" as often reported, merely deficient in essential elements.
Dunite includes about 3000ppm Ni, and about the same or higher Cr, about 500ppm Co, 100ppm Zn and Cu. Secondary minerals such as awaruite (Ni,Fe) may occur. In New Caledonia and Australia, the limonite formed is a nickel bearing variety garnierite which is one of the main ores of Ni. Associated with chromite lenses there also occur the platinum group elements, Pt, Rh, Ru, Os, Pd etc. The Merensky reef in South Africa contains half the world's known reserves of Pt and is a 2-3m band of chromite, leuco-norite etc within the Bushveldt Intrusion which is (however gabbroic or noritic) not peridotite.
The Red Hills lie along the eastern side of the Cascade river valley in South Westland and West Otago. The range is cut by streams originating in the schist range to the east which is covered in green birch forest, and which follow east-west faults which have offset the peridotite blocks up to a mile or so east-west. The first block at the north is a small outcrop north of the the Jackson River where it swings east into the schist range and terminated to the NW by the Alpine fault which follows the main Jackson River.. South is theJackson block, lying between the upper Jackson and the upper Martyr rivers. Next to the south of the Martyr headwaters is Martyr Hill which is about 2 miles wide by 3-4 miles long. Then the Woodhen Creek which separates the Martyr Block from the Mt Richards block which is about 5000ft high and separated by the McKay Creek from the
Mt Raddle Block. South of Mt Raddle there are two ridges of schist, peridotite being apparently absent until the Big Red Hill is reached lying on the west side of the upper Cascade River, about 600ft high and six miles long. At the contact with the schist to the east is Simonin Pass with the Red Pyke River to the west and SW.
A couple of miles on south is Stag Pass formed where a block of peridotite about half a mile wide by a mile long is inset in the range between the Red Pyke and the Barrier River. On the Barrier side is a small round flat half a mile across of deep red color, surrounded to the west, south and east by precipitous schist forest clad mountains. The Barrier issues west through a narrow gorge.
Beresford Pass occurs on the south side of the Barrier and has a very narrow strip 1-200 yards wide. Next comes the Diorite valley and then the Four Brothers Pass also formed by a narrow band of peridotite which includes some anorthosite, South again is the Olivine River which flows north before turning west under the Four Brothers Pass to tumble into the Pyke valley. The Olivine may be eroded along peridotite. A shelf to the east is called the Olivine Ledge but I have not seen peridotite in it, but it does crop out at the head of the Olivine valley at Fiery Col.
Three hundred miles north peridotite occurs again at Dun Mountain and geological maps show two thin bands extending north into the Sounds Country. Dun Mountain is thought to have been once continuous with the same rocks in the Jackson but to have been d isplaced by movement along the Alpine fault.
The Red Pyke River winds down a gorge from Simonin Pass into a low lying fault valley in which lie Lake Wilmot and Lake Alabaster. Finally about thirty miles south the Pyke (named for Vincent Pyke, an early surveyor) joins the Hollyford, and so to Lake McKerrow and the sea. New Zealand's last unspoiled land. Opposite Big Bay which lies to the right, is Pyke Hut, one of Davy Gunn's old huts when he ran cattle in these valleys and took tourists on tours with packhorses. A primitive airstrip was put in in the days when fortunes were made shooting deer and exporting venison to Germany. The strip is now overgrown with grass and flax but highwing C180's and C185's still land occasionally.
The west face of the Martyr block overlooking the Cascade out of sight, lower right. The peridotite shows prominent banding in the creek in the forground. The very black layer in the Y shaped tributary top left, might be chromititee, difficult to believe a pyroxenite could be so unaltered. Woodhen Creek lies in front of Mt Richards in the right distance.
This slab of infaulted peridotite lies between Otago Schists on left and Permian Livingstone Volcanics on right, which some assume has been partially melted out
of the peridotite. If so, the right contact MIGHT be part of the original Earths surface (or close to it). View South with Tutoko in distance, Stag Pass is at the junction of ther peridotite with schist to it's left and The Barrier stream lies ahead and below. The Upper Red Pyke and Simonin Pass lies below and behind as does Big Red Hill.