New Zealand Steel Mining Ltd TAHAROA REHABILITATION PROGRAM PRESENTATION. Reihana Chadwick & Greg Brown

Transcription

1 New Zealand Steel Mining Ltd TAHAROA REHABILITATION PROGRAM PRESENTATION Reihana Chadwick & Greg Brown Introduction by Greg Brown Taharoa Ironsand is mined, concentrated and exported from NZ Steel Mining Ltd Taharoa minesite located on the west coast of the north island of New Zealand 1

2 Introduction NZ Steel Mining Ltd is a wholly owned subsidiary of NZ Steel Ltd, which operates the Glenbrook steel mill. The Taharoa minesite is solely focussed on the export market into predominantly China and Japan. Mining began in 1972 and peaked in the mid 1980 s exporting 2.0 mtpa. Introduction Currently NZ Steel Mining Ltd exports are 1.0mtpa. 2

3 Mining & Concentration By Greg Brown The mining plant consists of a floating dredge which is an electro-hydraulically powered cutter suction unit, able to dredge to a depth of five metres below the surface at a rate of 750tph. 3

4 Mining and Concentration and Concentration plant (Wet Plant). 4

5 Mining & Concentration Mining is carried out by traversing the dredge across the pond using a system of hydraulic winches and wire ropes and spuds. Sand is then pumped 95m via pontoon monitor 15 hoses into the Wet Plant for concentration. Mining & Concentration The concentration plant consists of 4 separation processes. - Oversize removal (Trommell( > 2.5mm) - Primary gravity separation (cones) - Secondary gravity separation (cones & spirals) - magnetic separation 5

6 Mining & Concentration Concentrate slurry (Fe% %) is then pumped approx. 1 5 kms to the stockpiling area (Reihana will explain this in greater depth shortly). Tailings are disposed of using mobile stackers to re-contour mined land. 6

7 Shiploading By Greg Brown Concentrate is loaded onto the Taharoa Express through two parallel pipelines moored to a single bouy mooring (SBM) approximately 2.5kms off shore. It is fed from the conveyor into constant density tanks where it is mixed with fresh water to form a slurry (adjusted to 50% solids by weight). 7

8 Shiploading 127,000t is then loaded at a rate of 2700tph through the two underwater pipelines. Bulldozers push the concentrate onto a belt feeder and conveyor system under each stockpile. 8

9 Rehabilitation By Greg Brown The mining lease consists of approximately 1600 hectares divided into three distinct mining regions. Rehabilitation Mining began in the Southern region in 1972 and the resource was exhausted using the current plant configuration in late Mining commenced in the Central region in Feb 2001 with a current mine plan for 20 years. Mining was completed in the Southern most part of the mining lease approx. three kilometres from the Central region. 9

10 Plant Relocation A number of options were considered, the following was chosen. - To relocate the Dredge 250t - To relocate the Wet Plant 1000t Overland by truck. 10

11 Hand Over By Greg Brown Rehabilitation and handing back of Southern region to Taharoa C Block Corporation land owners. 11

12 By Reihana Chadwick Rehabilitation Of Southern Region Approx. 3mt of sand, dry mined from from the Rototapu dune. Production ceased in December 2000 and rehabilitation commenced. 12

13 Issues We Were Faced With by Reihana Chadwick No rehabilitation had been carried out since Approx. 150ha of land required contouring and planting. Three decant ponds behind the main pond had filled up with three metres of slime. The main pond, canal, dismantling pond, dry docks from the Plant relocation project also had to be filled in. 13

14 Issues We Were Faced With Required sand, had to be transported some metres to infill ponds. 14

15 Process by Reihana Chadwick Rototapu dune had been previously stripped of vegetation. Vegetation was stockpiled for approx. 12 months. Once dry mining of the area was completed, vegetation was redistributed over the land using dump trucks and then harrowed and bulldozed in (see photos) Process Stabilising tailings and decant ponds. Difficulty arose with in filling due to extent of slimes in all three ponds. Ponds were small in area by large in volume. Ponds were opened up in summer to allow to dry (left approx. one month prior to xmas). Areas similar to quicksand were common. 15

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17 Process Grass growth very good in areas with slimes. No planting was possible due to danger of sinking. 17

18 Infilling of Dredge Pond, Canal & Dry Docks by Reihana Chadwick Contractors on site using truck and shovel until dredge pond and canal half finished. Canal was filled with slimes settling out prior to use, causing difficulties. The southern region was re-contoured, ponds infilled and ready for planting of maram within nine months. 18

19 Infilling of Dredge Pond, Canal & Dry Docks Bund wall erected along seaward side of canal was used as infill. Large volume of sand left unused and pushed from up to 100 metres in places. Long pushes in most instances. A Windrow was left along seaward bund to provide shelter for shelter break when planting of pines commences. 19

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22 Maram Planting by Reihana Chadwick Grass is cut by hand taking roots to 0.5m under surface (cut from nursery). Bundled in 15kg bundles. Stockpiled in areas to be planted. Sand placed around edges to keep moist and encourage growth. 22

23 Maram Planting Four person team seated on a planter attached to the back of a tractor, plant two rows at a time. One tonne of grass planted per hectare. 70 tonnes planted in the southern region 23

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25 Maram Planting Historically, other plant types have been tried such as:- - Lupin to increase nitrogen content in soil, however these died due to disease. 25

26 Maram Planting Urea drops also used up until Now no fertiliser at all is applied. Once maram has established itself, other grasses and vegetation types can grown (usually within 12 months). Maram provides wind protection for other plant types. 26

27 Maram Planting Sand movement is also prevented by maram (up to 0.5 metres/week due to extreme winds. Pine trees are planted on reclaimed areas within two years. Re-distribution of the top 1 1.5m, removed prior to mining has also proved to be very successful. 27

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