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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