Mine Management Questions and Answers Series (1)

Question 1.

Figure 1. Represents all activities, starting from activity 1 to 12. Event 1 is the beginning and event 12 is the end of my task assigned (thick line represent critical path)

1.      Describe PERT/CPM network analysis, applications, advantages and disadvantages.

Project evaluation and review technique (PERT) is a project – scheduling  tool applied to ensure sequence of different activities eventually lead to a desired completion of a project in consideration. PERT techniques in network analysis is a method of minimizing trouble spots, production bottlenecks, delays associated costs, interruptions and reduce mis-allocations.

Advantages:

PERT is a planning and control technique that uses a network for scheduling and budgeting (time & finance) to accomplish a task.

Disadvantage:

The disadvantage in PERT network is that, an event cannot be accomplished until and unless all activities in a network have been completed. So in a PERT network, we are actually estimating the total project time. The path of the longest duration is called critical path and activities lying this path are critical activities. A delay in any of the activities in the critical path will result in delay, extra costs and resources, redesign, and re – routing of the entire project.

12.      What is the difference between an event an activity in a PERT/CPM network?

Activity is the task allocated to be accomplished towards the total completion oif the project on time. It is represented by an arrow. The tail of the arrow represents the beginning of the activity and its head represents its completion. Whereas,

Event is designation the beginning of one activity and ending of another activity. So the starting and ending points of activities are events.

23.      Describe how you would calculate earliest event (T_E) and latest event (T_L) times and define what they represent.

The earliest event time (T_E) is the earliest time at which the activities originating from an event can be started.

The latest event time (T_L) is the latest event time which activities terminating an event can be competed on scheduled.

So the earliest event time is calculated by adding earliest event time at the tail of activity arrow with the duration or earliest time of activity. Note that when there is more than one activity flowing into an event; choose the maximum value of T_Ej calculated for that event.

The latest event time is calculated by subtracting the T_L of the very last event by the duration/time for activity ij. Subsequently doing the same for rest of the events. When there are more than activities lead to an event, calculate and get the minimum value of T_L

14.      Determine the critical path of the exploration project schedule.

The critical path starts from event   1 to event 3 then to event 5 to 6, from event 6 to event 11 and ends at event 12. At these events the T_E value is equal to T_L at each event given above.

15.      What is a float and slack in PERT/CPM network and state why is having these advantageous in project scheduling?

  Float in PERT network is time available in the non – critical path that could be reallocated towards an activity in the critical path. It is advantageous having float because it represents underutilized time or underutilization of resources. Not only that but also float represents flexibility of an activity and disappearance of float signifies a loss of flexibility for non – critical path activities.

Slack in PERT network is the difference between the earliest and latest times of any event.  Slack is important as it help us to see whether it is a critical or non – critical path by analyzing the T_E and T_L values.

16.      Calculate head slack, tail slack, float, free float and independent float for one non – critical path activity (ij).

Tail slack Ts = T_si = T_Li - T_Ei = 15– 11 = 4 weeks (event 7)

Head slack HS = Tj = T_Lj - T_Ej = 29 – 18 = 11 weeks (event 7)

Float F = (TLj -  TEi) – teij = (29 – 11) – 7 =  11 weeks

Free float FF = (TEj – Tei)  - teij  =  (18 – 11) – 7 = 0

Independent float IF = FF – TS = 0 – 4 = - 4 weeks

Note: a negative independent float is taken as zero for all practical purposes.

17.      Briefly commend on your understandings of three extremes of expected times : (a) optimistic, (b) pessimistic  and (c) most likely time (m) as represented by normal probability distribution curves.

·         Optimistic – is the distribution that satisfy most circumstances at shortest times if execution goes very well.

·         Pessimistic – is    the distribution that satisfy most circumstances at longest times if everything goes bad.

·         Most likely - is the distribution that satisfies most circumstances at normal times or at middle grounds if execution is normal. In other words, it is the mean  of the distribution. 

18.      Complete the following table by calculating the variance (σ²).

Predecessor	Successor	a	M	b	te	σ2
1	2	3	2.5	5	3	0.11
1*	3	5	4.5	13	6	1.78
2	4	7	2	9	4	0.11
2	6	10	10.75	7	10	0.25
4	6	8	1	12	4	0.44
3*	5	5	6.5	11	7	1.00
5*	6	6	7.5	6	7	0.00
3	7	9	2.75	10	5	0.03
7	8	7	2	9	4	0.11
8	9	4	5	12	6	1.78
6*	11	8	12.5	14	12	1.00
9	11	2	5.75	17	7	6.25
7	10	11	5.75	8	7	0.25
10	12	3	14.25	12	12	2.25
11*	12	6	8	6	9	0.00

*critical path.

29.      Calculate Z (number of standard divisions), find corresponding probability value in Z table a conclusion on the probability of implementing your schedule as planned.

Sum of critical path σ² is = σ² _(1-3) + σ²_(3-5) + σ²_(5-6) + σ²_(6-11) + σ²_(11-12)

                                                 1.78  +   1        +  0       +  1         +  0

                                     σ²    = 3.78

                                         σ = (3.78)^0.5 = 1.9442

Assume X = 44 weeks, and µ = 41 weeks

Z = X - µ = (44 – 41)/1.9442 = 1.5431

         σ

Using the table (given), probability of success is: Z value of 1.5431 corresponds to probability of 0.4382 from the table. This means there is 0.9382 (0.4382+0.5) probability or 94% chance of completing the project in 45 weeks or less.

Basing on the probability analysis, I am too optimistic that the project will be completed in 45 weeks or less.

110.      Calculate the total float for the non – critical path.

Total float F_T = (T_Lj – T_Ei) – tij = (29 – 11) – 7 = 11 weeks (from event 7 to event 10)

Note that here, only one total float for only one non – critical path.  

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Mount Crater Gold Mine in Papua New Guinea

Crater Gold Mine is located in the western part of Eastern Highlands Province in Lufa District,
adjacent to the eastern border of Simbu Province bordering Kramui Nomane District. It is centered
50 Km southwest of Goroka, the capital town of Eastern Highlands Province.

The closest airstrip is the Guasa Airstrip. From Guasa airstrip it will take you about 2 - 3 hours walk up the steep hills and along the fast flowing rivers. The site is ussually assessed by shopper.

ML510 was granted to Anomaly Limited in November 2014 to carry out a small scale underground
mining and processing operation at Crater Mountain.

Prior to the Mining Application and due processes were followed for granting, there was an exploration license EL 1115 which was known as Nevera and Nimi Prospects. The exploration could have started long ago back in the 1980s and various  PNG National geologists as well as foregne geologist can recall this prospect. The EL 1115 started in 1994 when the exploration licence was granted initially to MACMIN and then jointly explored by BHP. It was then to Anomaly Limited. Anomaly then tirelessly continued the exploration until the mineral resource was defined and further intended to apply for a mining lease to developed the ore body which was defined.

Mineralisation is typically confined to veins and thus dictate the Mining Method to be sub-level caving. The operation utilities hand-held  rock drills and jack picks. Broken ore is transported via mini rail cars to surface for processing.

Tailings discharge from the mill is collected in a sump where solids settle and the water overflow is
channelled into a second sump to further settle any silt and clear water overflows out to the nearby
creek. The solids in the sumps are harvested periodically and stockpiled for further processing at a
later stage.

Thus, it is believed that mine waste is managed within the vicinity and less environmental impacts are anticipated in this operation.

Photo Courtesy of Anomaly website

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APEC Mining Task Force Chair Pays visit to Mineral Resources Authority (MRA) of Papua New Guinea(PNG)

Following a hectic APEC first Senior Official Meeting (SOM 1) meeting held in Port Moresby from 5 – 6 March 2018, the APEC Mining Task (MTF) Force Chair from Chile, Mr Rodrigo Urquiza Caroca made time available on 6 March, 2018 to visit the Mineral Resources Authority and the MTF team. He was introduced to the staff of the Regulatory Operations Division by the Executive Manager, Mr. Roger Gunson.

The APEC MTF Chair plays a key role in coordinating MTF activities within APEC economies that are associated with mineral trade and investment, governance, best practices and policies.

The visit was timely for the MRA as it discussed preparation for the upcoming APEC Mining Week, which is scheduled to be held this year in the APEC third Senior Official Meeting (SOM 3) from 17 – 25 August, 2018.

The APEC Mining Week features key sessions involving public private dialogue on mining issues and best practices in the APEC economies, mining companies CEOs meeting and APEC economies’ Minister Responsible for Mining meeting.

Mr. Caroca was then taken to Motukea wharf to see under water mining equipment. He was impressed to see the level of advance PNG made in terms of innovation and technology in its mining sector.

Mr. Caroca was presented PNG gifts, which include a cane woven tray, two hand-made highlands Bilums (bag) and a packet of local PNG coffee.

Mr. Caroca thanked the ROD’s staff for the gifts and he said he will take them with him to Chile.

Roger Gunson- EM ROD(Left) presenting the present to Mr.Rodrigo Urquiza Caroca(Middle) and Chief Mining Warden of MRA, Mr.Andrew Gunua(Right), 

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Description of Gold

Gold is a soft yellow metal which is much heavier than a normal stone of the same size. It is non-corrosive, non-magnetic. However, gold is very good conductor of heat and electricity and it does not change its state or color even when exposed to the nature for millions of years.

Gold is valuable and can be a substitute for money in trade. Gold is like money and it is used as a financial instrument and is readily traded throughout the world. It has a well-publicized price. Gold is mined and recovered by utilizing different mining and processing techniques. 

It can be mined by locals using small scale mining methods for alluvial or mined from hard rock gold deposits using highly mechanized operations or from placer deposits using simple or semi mechanized alluvial mining techniques.

Some minerals can be misleading. i.e. pyrite will look similar to gold but you need to know very well the properties of gold in terms of shape patterns and appearance. Pyrite is actually a fools gold.  First timers need to be very careful if you are buying gold from alluvial gold miners. There are other various techniques which you can use to identify and be sure that what you see is for sure gold. Stay in tune or subscribe for updates on the next article(s)

Photo Courtesy of Gem Rock Auction

Reference:

Small Scale Gold Mining in Papua New Guinea, Department of Mining Papua New Guinea 2001.

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Environmental Impacts of Artisanal and Small Scale Gold Mining in Papua New Guinea

Mechanize Small Scale Mining

Artisanal and small scale gold mining (ASSM) offers lucrative employment opportunities to the locals of most developing countries. The major drawback of ASSM is its impacts on the environment as a result of improper mining and processing techniques. Exposed and disturbed lands are usually subject to soil erosion and avalanches of debris in active ASSM areas. Mercury is commonly used to concentrate gold, and if not handled properly causes pollution of life supporting river systems.

Small scale gold miners in many developing countries rely primarily on deposits containing free gold and may be classified as shallow/deep alluvial or lode type. The mining method used in artisan small scale gold mining employ very basic technology. Shallow alluvial deposits are commonly found in valleys and streams at depths not more than two meters. Deep alluvial deposits are found along major riverbanks and older river courses, and usually at depths exceeding six metres along the banks of rivers. The lode type of gold deposits is usually composed of partially weathered gold bearing reefs, which are either outcrops or near surface deposits. In Papua New Guinea, active artisanal mining are commonly found abandoned mining areas like Panguna and Missima and also near operating mines like Porgera, Eddie Creek in Wau Bulolo, Morobe Province. Not only that but also other parts of the Provinces also have active small scale miners. Other provinces include but not limited to: East Sepik, Sandaun, Enga, Western, Eastern Highlands, Jiwaka, Madang, Western Highlands, Oro, Milne Bay,Morobe.

 The small scale gold fields are mainly riverine deposits where mining occurs along river banks, terraces and in active river channels. Using poorly constructed sluice boxes, gold bearing material is fed into the inclined sluice boxes. The box is constructed using plywood or flattened roofing iron with wooden/metal ripples. These types of operations are associated with low to very low recovery because of uncontrollable river flow rates, incorrect inclination of the sluice boxes and inappropriate amounts of feed material at any one time. It is extremely difficult to introduce mechanised alluvial mining because of low skills and knowledge, isolation from transport infrastructure and lack of basic infrastructure.

The gold bearing gravels are concentrated by rippled sluice boxes. The fine gold is not commonly trapped in the ripple compartments. The fine particles of sand with gold in it are than poured into the panning dish for further panning. Mercury is placed in into the panning dish to concentrate the fine gold particles. Amalgamation is an efficient mean of extracting gold particles from concentrates after panning or sluicing.

In PNG small scale mining operations, the concentrates from sluicing operations are mixed with mercury in gold dishes or in sluice boxes. Mechanised concentrating equipment like the shaking table and Nelson concentrators are other options that few small scale miners are looking at. 

Health and environmental impacts (Watch Video)

The artisanal and small scale gold mining provides employment at local and national levels, and the sector is an important source for the inflow of foreign exchange into rural communities. However, small scale mining activities are associated with sensitive health and environmental issues.

The process of recovering gold by retorting and heating the amalgam over an open fire is a dangerous practice. The open fire could be in houses or at river banks and thus a whole family could be exposed to poisonous mercury fumes.

Concentrate from sluicing near streams is usually mixed with mercury and a considerable amount of mercury is lost to the streams. Apart from direct inhaling of mercury fumes by miners, aquatic life also feeds on mercury lost into the river, which are then eaten by the locals through the food chain. The Watut and Bulolo Rivers has been subject to prolonged mercury contamination and discharges of hydrocarbon wastes. The Watut people depend on the river for fishing, washing and farming on the river banks.

Some miners in old shafts and adits and they are consequently exposed to the trapped noxious gases such H2S. Locals have been reported that they are buried alive when they burrow through soft oxidized lodes or vein systems.

Some operators locate their sluice boxes in streams, thus polluting the water. Silting and stream discolouration are very common. Farmlands are usually destroyed by mining activities. Locals even uproot big trees along structurally defined thin gold deposits. Sometimes, the narrow gullies are not rehabilitated and are left to be taken care of by nature.

Exposed and disturbed lands are subject to soil creep widening the flow channels, and debris avalanches are common along rivers at the active mining areas. The loss of fertile land due to small scale mining puts socio-economic pressure on the local society. Old gravel pits are usually abandoned without reafforestation. Pits filled with stagnant water are common.

Education and training

Small-scale mining technology in most developing countries is simple and attracts many unskilled people. The desire for economic and social survival has attracted many people to the industry. The law expects the licensed small-scale miner to mine using effective and efficient methods, and observe good mining practices, health and safety and protect the environment.

The Small Scale Mining Branch of PNG Mineral Resources Authority (Formerly Department of Mining) in Wau, Morobe Provine has created education and training materials for the miners. The Department has produced seven booklets and DVDs on

• Simple Gold Mining;

• Basic Mining Practice;

• Advanced Mining practice;

• Handling of Mercury;

• Occupational Health and Safety;

• Environmental Issues; and

• Economics of Mining.

The major focus of the training resources is to ensure that small scale operations are safe, environmentally friendly and economically viable.

Small-scale mining operations in most developing countries have serious negative environmental impacts. One of the major factors is the implementation of the associated mining Acts  which are lacking.

Donor agencies like the World Bank, European Union and Japanese International Cooperation Agency (JICA) have in recent times shown keen interest in the negative and positive impacts of the PNG’s ASSM sector. AusAid and the World Bank have sponsored the building of the ASSM sector capability in PNG through legislative framework and training and awareness on the use of mercury.

Note: This article is a reproduction of a learning material with inclusion of up to date information.

Reference

[1] Ail, K. K. (2005. Kwoe River Alluvial Gold Deposit Evaluation and Development Plan, PNG University of Technology, Lae.

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Osarizawa Mine in Akita Prefecture, Japan

Osarizawa Underground Mine Adit

Osarizawa mine is an abandoned mine in Akita Prefecture, Japan. Event though the mine is closed, the mine site is kept for sightseeing purposes.  The Osarizawa mine deposit is a vein type deposit  which was  discovered in 708. The oldest Literature of the mine was written in 1599 about the discovery of the Gojumaizawa gold deposit which is part of the mine. The main commodities produced by the mine were gold and copper.

The vein deposit was mined using the shrinkage stope mining method. There are 15 levels and are 30m apart in height. The Total perimeter of the mine levels is 700 km. The area of the mine site is 3km N-S by  2km E-W ~ 6km² . Ceiling is 2-3m in width.   

The Level Zero starts at RL of about 300m and this is where the access adit (ingress) is built.  There are 5 levels above the  zero level and 10 levels below zero level. The mining progressed upwards and mined materials were collected at lower levels with the aid of gravity.

The host rock of the ore deposit is silicate mudstone which is 10 times harder than concrete. Since the host rock is highly competent, the mine was almost unsupported and less artificial support. Few supporting materials used were logs/timbers of about 10mm to 300mm in diameter which were fitted well in between mined out areas to prevent wall collapse. Other artificial supporting methods are roof bolts, Mass wires and steel spiral cables drilled upwards to prevent rocks from falling. Timbers are replaced every 10 years. The other supporting method used was the backfilling of mined out areas with waste materials. Underground water is effectively under control by plastic roofing gutters and drained out along the side of the concrete pathway at each level.

The mined out ore/materials were transported by mini rail cars which are powered by batteries. The rail cars were attached to one another like train cars. The railways were built for these small battery powered rail cars. The drilled or broken ores were loaded onto the rail cars and it required either one or two operators to transport the materials out of the mine via shaft by way of hoisting. At Zero Level the rail cars were driven out via the adit and further to the processing plant for processing.

 Production increased with the increase in the rail cars.

Note:This article is an observation report and may not contain factual and detail information. The information here is kept at high level only. This article is subject to change if need be.

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