Mineral Exploration - Science topic

We have done geomagnetometric studies on some porphyry deposits in different parts of Iran and also we reprocessed some previously acquired geomagnetic data on porphyries.

Contrary to popular belief, I can tell you magnetic data layer is one of the best layers for the delineation and study of porphyry deposits but the interpretation of magnetic data needs a deep understanding of economic geology and geophysics.

In most of our cases, low magnetic responses were the target rather than high magnetic anomaly zones.

The following items are crucial in porphyry magnetic responses:

An interpreter should consider all of these items for geomagnetic data interpretation. As an example for highlighting the effect of flight height, a potassic alteration which was showing a positive magnetic anomaly response in ground-base magnetometry, was showing low magnetic anomaly when we analyzed its airmag response!

So a lot of factors should be considered.

But based on our experience Analytic signal and Upwarded Analytic signal method is one of the best operators for the delineation of target areas that are susceptible for porphyries. We tested it in different porphyries and the results were great.

So if a geophysicist comprehensively considers the parameters, the Analytic signal can delineate target zones even in low erosional level porphyry and masked ones.

Dear Mehdi Masoumi, can you help with how to install EnMap box on the ENVI program? Thanks

Regards

Of course...that is how scientific exploration works. Otherwise you have to keep re-inventing the wheel. The real question is not "type" but what you say about it. I attach a little "cartoon" I made regarding a major porphyry copper deposit in Chile. Having proposed a coherent geological mechanism involving a mine and a process...in this case copper bearing magmatism associated a proposed tectonic detachment feature, now I try to tie local deposits together. They may all be different types but they might fit into a larger process that you can use to predict or explain. You might find skarns here and dikes there or the remnants of a leakage pattern in a "fault" but they are part of a whole...assuming, of course the respective age dating allows it.

Dear Saifur Rahman Khan and Al,

lI wish you Happy New Year: success in your spiritual achievement, good health and prosperity for it!

I found the next on the facbook (https://www.facebook.com/USGSVolcanoes):

'A volcanologist is a person who studies volcanoes, but there are many different specialties within the field of volcanology. Which interests you and what steps should you take to achieve your goal? Find out more in #VolcanoWatch.

Earthquakes are one primary tool used to study volcanoes. A volcano seismologist studies the earthquakes that are generated as magma moves through Earth’s crust.

A volcano geodesist studies the deformation, or change in shape, of a volcano caused by the movement of magma and gases beneath the surface. Many features of volcanoes can be studied from space, as well, using satellite sensors. Tools like these provide clues about the state of the volcano.

Geologists and geochemists study the composition of lavas and gases to understand the source and style of the eruption. Measuring gas emissions is especially important, as the vog (volcanic air pollution) caused by toxic volcanic gases can contribute to breathing problems, acid rain, and agricultural problems downwind, especially during long-lived eruptions.

If you are interested in becoming a volcanologist, you’ll need to work toward a bachelor’s degree, preferably in a STEM field (Science, Technology, Engineering, and Math). Volcanologists frequently pursue degrees in geology, chemistry, physics, and/or mathematics, but that is not always the case. Oceanography, computer science, engineering, environmental science are all potential pathways, and the list goes on. Explore different fields to find what interests you most.

After achieving a bachelor’s degree, consider options for advanced degrees like a Masters or Doctorate. Many advanced degree programs in the sciences are funded, meaning tuition may be waived, and you might get a stipend for doing the work. Basically, you get paid instead of having to pay for school, and you gain valuable work experience at the same time.

You might consider working for the USGS or other agencies and companies. You have seen many photos of HVO scientists working during the eruptions of Mauna Loa and Kīlauea. The National Park Service also offers a variety of positions for people with either bachelor’s or advanced degrees, such as park geologists, archaeologists, botanists, guides, interpretive rangers, and law enforcement rangers. Science writing and journalism are also excellent ways to explore the excitement of volcanology, natural disasters, and cutting-edge science, while encouraging those passions in others. Similarly, eco- and geo-tourism are great ways to get close to the action and work outdoors, while also meeting, educating, and inspiring people from all over the world. Careers in emergency management will have you helping people stay informed during crises.

Check out usajobs.gov for positions within the federal government. There is even a special section for students and recent grads.

Volcano Activity Updates

#MaunaLoa is not erupting. Webcam imagery shows weak, residual incandescence intermittently in the inactive Northeast Rift Zone fissure 3 lava flow at night. Seismicity remains low and ground deformation rates have decreased. Sulfur dioxide (SO2) emission rates are at background levels. For Mauna Loa monitoring data, see: https://www.usgs.gov/volcanoes/mauna-loa/monitoring-data.

#Kilauea is not erupting. Lava supply to the Halemaʻumaʻu lava lake in Hawai‘i Volcanoes National Park ceased on December 9. Sulfur dioxide emission rates have decreased to near pre-eruption background levels and were last measured at approximately 200 tonnes per day (t/d) on December 14. Seismicity is elevated but stable, with few earthquakes. Over the past week, summit tiltmeters recorded several deflation-inflation (DI) events. For Kīlauea monitoring data, see https://www.usgs.gov/.../past-week-monitoring-data-kilauea.

There were three earthquakes with 3 or more felt reports in the Hawaiian Islands during the past week: a M3.3 earthquake 14 km (8 mi) S of Fern Forest at 7 km (4 mi) depth on Dec. 27 at 4:33 a.m. HST, a M3.4 earthquake 7 km (4 mi) WSW of Volcano at 2 km (1 mi) depth on Dec. 24 at 8:31 p.m. HST, and a M2.5 earthquake 1 km (0 mi) S of Mountain View at 11 km (7 mi) depth on Dec. 24 at 9:57 a.m. HST.

In the photo, an HVO technician adjusts a volcanic gas analysis instrument that was specifically designed for this Unoccupied Aircraft System (UAS) unit, which carries three one-liter analysis bags. The instrument transmits gas concentration information in real-time during the flight at Kīlauea summit. USGS has special use permits from the National Park Service to conduct official UAS missions as part of HVO's mission to monitor active volcanoes in Hawaii, assess their hazards, issue warnings, and advance scientific understanding to reduce impacts of volcanic eruptions. Launching, landing, or operating an unoccupied aircraft from or on lands and waters administered by the National Park Service within the boundaries of Hawai‘i Volcanoes National Park is prohibited under 36 CFR § 1.5 - Closures and public use limits.

USGS image taken January 14, 2022 by M. Warren.

#USGS #HVO #HawaiianVolcanoObservatory'

Maybe it can help you!

Regards,

Laszlo

Dear Mr. Sarco:

You have to distinguish between two types of exploration.

Geochemical exploration means systematic sampling and analyses of inorganic and organic natural material to detect anomalous concentrations of elements derived from mineral deposits. The element concentrations are plotted on maps and contoured at different intervals to delineate anomalous areas

1. Geochemical anomalies may be due to primary processes when an ore deposit was emplaced under high T and P conditions

2. Geochemical anomalies may be due to secondary processes when an ore deposit is exposed by weathering and erosion and the constituent minerals and trace elements are dispersed and transported downstream

1. is impacted by surface- and groundwater having been derived from the supergene and hypogene zones and controlled by soil and litho-hydrochemistry

2. is impacted by surface water having been derived from the supergene zone only and controlled by soil hydrochemistry

Marker- or pathfinder elements in hydrochemistry are

• Au Ag, As, Cu, Pb, Sb, Zn

• Co As, Cu, Ni

• Pb-Zn Cd, Ba, Hg, F, As, Sb, Mo, V

• „Kieslager“ Se, Hg

• Cu Mo (porphyry-type), B (skarn-type, Co, Ni, As, Pb, Zn)

• Pegmatite Li, K/Rb

• Sulfide ore Ag, Bi, Sb, Hg

• U As, Mo, Se (red bed-type deposits)

HGD

The last resort is to take a list of companies mining Fe on a worldwide basis. There are lists of almost all important producers with contact adresses (E mail etc.). Then direct your personal requests to them and in the majority of cases you will get the hottest data better than in some mining journals because talking to colleagues worldwide face-to-face via E mail or even by exchange of mail may get you closer to your target than browsing the internet. This is my personal opinion. We did something like that many years ago (study of quantifying the amount of substances from the pit to the product).

HGD

Visit kindly the following useful RG link:

Thank you very much, Dr. Berkman. Let me share, please, an additional comment.

There is an aspect of your query that is more relevant and is alerted by Ernest Berkman's response: the distribution of reading points should be homogeneous in distance since there is a relationship between the wavelength of the anomalies and the distance between points. Therefore, over the whole interpretation progression after the grid's operations.

When you add more grid points in your gridding achievement, it is possible to change the lateral accuracy: More points you add, more frequencies you can resolve tending towards a better spatial solution. Therefore, the solutions you plot are not rigorously comparable. You can see also the radial average power spectrum content in the wavenumber space as a further comparison. In this sense, a larger grid cell size (filter width) correctly smooths the solution. You should compare please in the example that I attached: as the same area, there are two surveys: one regional and another high-resolution. Even the low and high anomaly distribution is similar, there is more confidence in the map or grid with the lower cell size. The Nyquist spatial frequency and wavelength are affected by the number of points by unit area and its relative distribution. That is:

The Nyquist spatial frequency f = 1/(2*grid spacing). Multiply that by the cutoff fraction (e.g., 0.5) then divide 1 by that number to get the resulting wavelength.

More concisely, cutoff wavelength = (2*grid spacing)/(cutoff fraction).

Best regards, Mario E. Sigismondi

The transition to a circular economy is not uniform and varies depending on a series of factors such as the degree of industrialization, the level of technological development, the availability of qualified human resources and access to financing, among others.

As with all geological systems you need to understand the data and let the data inform the interpretation, not make an interpretation then use the data to support it.

Many studies have reported Pb-isotope analyses with the data used to: develop standards, global and terrain-specific growth curves and dating techniques (Cooper et al. 1969, Cumming & Richards 1975; Stacey & Kramer 1975, Gulson 1984); to distinguish between groups of deposits within a single terrain (Stanton & Russel 1959, Cannon et al. 1961, Gulson & Mizon 1979, Gulson et al. 1985, Carr et al 1995 etc); and, to highlight the time difference between lode formation within a single system (Broken Hill, Pinnacles; Parr et al. 2004).

Lead isotope studies can provide insights into tectonic and mineralising events and improve the understanding of events within a given terrane (Carr et al 1995, Huston et al 2016). Major magmatic, thermal and hydrothermal events typically result in the loss of 238U, 235U and 232Th and homogenise Pb isotope values unless overprinted by later high-Pb events, or by the addition of radiogenic Pb (Doe & Stacey 1974; Faure & Messing 2005). The addition of radiogenic Pb may modify the initial ratio of a sample, leading to Pb isotope signatures higher than the initial (primary) ratio (Cannon et al. 1961). In high-Pb samples, including galena and samples with >700 ppm Pb, there is generally insufficient 238U, 235U and/or 232Th present to significantly change the “initial” Pb-isotope value through radioactive decay (Gulson 1986) 9although there are exceptions - the MVT mineralisation in the Adelaidean overlying the palaeoproterozoic Broken Hill area). By contrast, for low-Pb samples the breakdown of even small amounts of 238U, 235U and/or 232Th may (and often will) significantly change the “initial” Pb-isotope ratio and such samples need to be treated with caution.

Pb isotope data is a powerful tool in the identification and discrimination of mineral systems. However, you need to understand what you are trying to establish. For example, If you are trying to discriminate between gossans and/or high Pb soil anomalies resulting from the weathering of mineralised veins vs false anomalies resulting from weathering related processes you need to have data from both the target system as well as the zones that you are interested in (see Gulson 1986 and related papers). However, as clearly demonstrated in a recent paper by Fitzherbert et al (2019) for the Cobar Basin NSW Australia, you need to be careful. New dating of mineral systems in the Cobar Basin supported by high precision Pb and other isotopic data has clearly shown that instead of a single mineralising event there was a near continuous series of events with mineral systems evolving and telescoping, often within the same structure over a 40 My period with epithermal > intrusion related Cu-Au > reduced basinal fluid Pb-Zn systems with systems migrating spatially over time. It took the combination of high precision dating using several techniques together with high precision Pb isotope data to resolve the what was happening over a +150km zone that hosts a massive amount of metal.

Having worked on many Pb isotope datasets over a 30 year period, some words of caution:

Peter

Carr G.R., Dean J.A., Gulson B.L. & Suppel D.W.1991. Lead isotope signatures of Ordovician to Permian mineralisation in the Lachlan Fold Belt — genetic and exploration implications. Geological Society of Australia, Abstracts 29, 6.

Fitzherbert J. A., Downes P. M., Blevin P. L., Huang H., Matchan E., Waltenberg K., Wall C. & Phillips D. 2019. Refining the Cobar-type mineral system: new insights spawned from direct dating of mineralisation. Discoveries in the Tasmanides 2019 (Mines and Wines 2019), AIG Bulletin 69

Gulson B.L. 1986. Lead isotopes in mineral exploration. Amsterdam, Elsevier, 245 pp.

Huston D.L., Champion D.C., Mernagh T.P., Downes P.M., Jones P., Carr G., Forster D. & David V. 2016. Metallogenesis and geodynamics of the Lachlan Orogen: new (and old) insights from spatial and temporal variations in lead isotopes. Ore Geology Reviews 76, 257–267

You have two options to use, field or laboratory methods.

In the field there are only handmagnets (Type Wilke) for different field strength values with adjustible working distances (for separation of Fe oxides, Fe-(Mg) silicates) , etching with HCl and and alkaline solutions such as (KOH) mainly for alteration zones and a couple of pycnometer and balance to determine the specific gravity of minerals which covers a rather wide range. These field method which needs some experience are good for grouping of mineral groups (ferromagnetic-diamagnetic..), solubilities and density. I have a so-called "Emergency kit for applied geosciences" which contains all these items and more, e.g., (hand) lenses of larger magnification Moh´s hardness set, UV lamp, diamond tester (useful also for topaz, corundum varieties etc,). I have built up the kit over a long period of time along with increasing practical experience gathered in the field mainly for heavy mineral exploration and soft rocks.

It may be enough for exploration but it is insufficient for a precise identification which can only been done in the lab using polished sections - see Dr. Grundmann´s suggestions-, XRD, SEM-EDX/WDX, and EMPA.

HGD

Aster is great and free ! Methodology is same as my article

Dear Subhendu: please, let me share this landmark comments by Alan B. Reid and Jeffrey B. Thurston (The structural index in gravity and magnetic interpretation: Errors, uses, and abuses Alan B. Reid and Jeffrey B. Thurston, Geophysics, Vol. 79, No. 4 (July - August 2014):

Abstract:

"The structural index (SI) is based on the concept of Euler homogeneity, a description of scaling behavior. It has found wide use in potential-field depth estimation and is a constant integer for simple sources with single singularities (points, lines, thin-bed faults, sheet edges, infinite contacts). For these cases, the SI is identical to the index of a simple power-law field falloff with distance. The simple Euler formulation is only strictly correct for such simple sources and integer SI values. The widespread use of the simple Euler method on more complex structures, using fractional SI values is likely to produce misleading results because the SI is no longer a constant for any given source."....

Also, I attached "Comment on ‘A crustal thickness map of Africa derived from a global gravity field model using Euler deconvolution’ by Getachew E. Tedla, M. van der Meijde, A. A. Nyblade and F. D. van der Meer", article that was written by Reid, Ebbing and Webb in Geophys. J. Int. (2012) 189, 1217-1222. Please, read the point 3.3 Choice of structural index, and Conclusions "... The use of the Euler deconvolution method as applied by Tedla et al. (2011) does not provide new and useful results, but merely demonstrates that potential field data can produce misleading results, if used without proper understanding..." Learned lessons, that warn us to avoid the same mistakes.

Mario E. Sigismondi

Dear Rameshchandra Phani: You asked for a photomicrograph of carbonate ocelli in a lamprophyre, here I attach some, and also panoramic views of the whole rock, and inversely zoned hornblende, all from the lamprophyres of Paraguaná Peninsula. Regards, Sebastián.

Dear Mr. Kasay:

I can offer you a flow sheet to obtain mineralogical results from a combination of mineralogical and chemical analyses

1. Check your bulk samples with a gamma scintillation counter to see if Th or U minerals are to be expected

2. A rock chip is used for thin section examination of the regolith, lateritic crust…. for textural and mineralogical analysis

3. Bulk chemical analysis of the rock sample using XRF (LREE are normally obtained at a reliable level). For more detailed analysis you need e.g. neutron activation….

3. Part of the grinded material used for preparation of samples for XRF is shipped to a laboratory

for screening and to split into the particle range < 63 µm and 63 µm to 300µm.

4. The interval < 63 µm is suitable for XRD (in case of detailed clay mineral analysis the use of settling tubes is recommended)

5. The grain size interval 63 µm to 300µm forms the basis of the separation of heavy minerals and for further investigation see point 6

6. The fraction separated under point 5 can be used for XRD (Rietveld), EMPA, SEM-EDX (+MLA) or (micro) Raman analysis of accessory minerals as they are common in the regolith on top of carbonatites

All data can be plotted into triplots and x-y plots for mineralogical and chemical discrimination.

Dependent upon the availability you can stop and leave this sequence at any point.

I wish you much success H.G.Dill

Dear Subhendu Mondal, glad to meet you!

Your question is very useful to remember us some issues related with the gravity and magnetic interpretation.

First, it is tacit that gravity and magnetic data cannot be interpreted uniquely in terms of depth; even when the density or magnetic susceptibility contrast are strong or weak, a whole family of configurations can be found for the interface contrast, at various depths, and any one of which will satisfy the observed gravity / magnetic data.

I divide my answer in four parts, following your own words:

1) When you write: “…2D subsurface model…”. Please, you must remember that the real profiles from maps are not in 2D: they are 2.5D. This is an important concept. If you are working at GM-SYS modeling tool, you must to choice the gravity observation and / or magnetic observation profiles: the real data, and each one you change your model (density contrast, depth, shapes of the anomalies) the curves of your gravity model and / or magnetic model changes. The challenge is trying to do your best model for the convergence of the model with the observation data.

2) When you write: “…i am using residual anomaly…”. As a Geophysicist interpreter, I must say to you that nowadays, and in the past too, it is not possible to reach a whole discrimination of gravity / magnetic anomaly map / profile into the contribution of:

1- the regional

2- the residual

3- (plus, the noise)

because their power spectra overlapping.

If you are talking about residual data, therefore, you applied before an upward continuation, and also, a continuation distance of one grid cell is not uncommon, although you should be critical of how much resolution you are losing in the smoothed data when you choose the upward continuation distance. This is your choice, again, as a the better person who know the geology and target of your work.

3) When you write: “…which will be the maximum depth value for preparing the model with better accuracy?” As Interpreter, you can drive the maximum depth tolerance to allow (percentage) (default value is 15). Therefore, all depth-solutions with error estimate smaller than this tolerance will be accepted. A smaller tolerance will result in fewer but more reliable solutions.

I recommend trying to do before a spectral analysis (remember limitations that I said in point 2), and you will have an estimation of the shallower average sources of your zone of interest by measuring the slope of the energy spectrum and dividing it by 4pi. A typical energy spectrum for gravity / magnetic data may exhibit three parts – a deep source component, a shallow source component, and a noise component.

An additional argument: we do not escape the ambiguity: in fact, gravity and its derivatives are related by a result of Green’s theorem, that provides an analytical proof of ambiguity not only for gravity but also for magnetic as well.

Also, remember that there are a wide variety of gravity and magnetic surveys, as a function of the terrain clearances, sampling rates, line spacings … and your spectral analysis is reflecting not only these condition (acquisition) but also: the choice of your grid-cell-size (interpretation) e.g.: this should normally be ¼ to ½ the nominal data sample interval.

4) When you write: “…is there any thumb rule in this case?"

The best rule is trying to do

1- spectral analysis,

2- profiles in GM-SYS or similar;

3- inversion profiles, and

4- compare it with another solution, such as: Euler deconvolution, SPI, Werner, AS, and, of course, if you have: seismic and well-logs control.

It should be emphasized finally, that, regional - residual (local) separation that describe large-scale-deep structure and small-scale-shallow structure, respectively, you and me must be considered in terms of the scale of the survey; also, I recommend to you to define the regional as the effect in which you are not interested. Maybe for you the regional is different that my criteria.

Best regards, Mario E. Sigismondi

Nitesh Patidar Thx for your suggestions!

Hi Ronak, there is an interesting article for you. It is accessible online: Atzori S, Salvi S (2014) SAR Data Analysis in Solid Earth Geophysics: From Science to Risk Management, DOI: 10.5772/57479

There are many key minerals that helps in exploratory work and identification of fertile vs. barren plutons in case of primary magmatic deposits. While speaking about the plagioclase, the mineral chemistry helps most in identifying a fertile granite from its barren counterpart; for which EPMA profiling of plagioclase is necessary. For example, plagioclase from fertile and barren systems can be effectively discriminated on a diagram of anorthite An% versus Al/(CaCNaCK) (calculated on the basis of atoms per formula unit (a.p.f.u.). You can consult the paper by Williamson et al., 2016; on a title, 'Porphyry copper enrichment linked to excess

aluminium in plagioclase', published in Nature geoscience (Letters), Link ONLINE: 1 FEBRUARY 2016 | DOI: 10.1038/NGEO2651.

There are many more such attempts made by other workers. A detailed literature search is needed to have a clear idea based on the rock type you are working with.

Good luck to you.

D. Majumdar

Dibrugarh University, India

Dear Puria,

Perhaps, the next ideas not so good does, but they are original, without any trick: We know well that exist three important type of Sulphur isotopes from all 26 isotopes.

‘Sulfur (16S) has 24 known isotopes with mass numbers ranging from 26 to 49, four of which are stable: 32S (95.02%), 33S (0.75%), 34S (4.21%), and 36S (0.02%).’ Wikipedia: https://en.wikipedia.org/wiki/Isotopes_of_sulfur

From the attached link we can conclude that the only four Isotopes of S has geological importance (32S; 33S; 34 S 36S) You do not need anything to compare them First (with U and Th isotopes) after it with REE elements) you will get a very important and useful results and from them conclusions (I do not verified that exist literature about such a works, but exist no tested ideas which can help you to make your PhD…

If you are going this way you will have better solution to make a good professional carrier like in other case but the knowledge of some no conventional secrets is no problem …

Regards,

Laszlo

P.S. You have gotten a good (practically better like mine) posts before from: Landry Soh T. Jaloul Bejaoui, Dipak C Pal , too!

Louis,

I would fully endorse your suggestion that you should be involved with this project, although I am not a project member myself. The Kivu region of eastern DRC has now become a critical area to study for understanding the Mesoproterozoic evolution of the greater Congo craton (CBT craton), as, if the Kibaran oceanic suture that Kampunzu and Rumvegeri proposed does exist, it should be in this area rather than in Burundi or Rwanda. Although the Mesozoic-Cainozoic western rift valley intervenes between them, making correlations particularly difficult, I think that the area of NW Burundi and SW Rwanda that you have studied is an important transitional area towards the Kivu Belt.

Note that I believe that there are already problems with correlating stratigraphic units from the better constrained eastern Burundi (Muyinga and Ruyigi) areas to the western parts of Burundi (Cibitoke and Bubanza). This is mainly due to the greater incidence of both granite intrusion and later faulting (Neoproterozoic and Phanerozoic) in the west. I also believe that the current division line between the Kagera and Akanyaru Supergroups (which currently runs along the top of the Muremera quartzite unit in most of eastern Burundi and its equivalents in NW Tanzania) is misplaced and probably should lie more to the west, coinciding more with the major N-S tectonic "accident" or shear/thrust belt associated with the Cene quartzite. This opinion is based on interpretation of regional geophysical surveys as well as mapping in eastern Burundi and NW Tanzania.

Although the bases of the regional geological mapping were completed in the 1960s to 1980s in Burundi, Rwanda and Kagera region of Tanzania, which have been supplemented by the high-quality zircon geochronology of Tack et al 2010 and Fernandez-Alonso et al 2012, there is still more that can be done in terms of relating datable metamorphic and hydrothermal events to the regional structural-stratigraphic context. This will be important to carry the correlations by accurate and reliable absolute age dating techniques from the eastern side of the belt to the western side.

Best wishes,

Dave Evans

 Hi Miłosz, it is good idea to offer your services here but I found that this should be a targeted offer to those who may be interested. You should really make separate project, name it, collect references to publications on related research subjects, then gather interest that can be converted in requests for your services. Indeed, this is not a good place for business offer. You should get all these possibly interested colleagues into Facebook or LinkedIn to discuss business. Good luck! P.S. I worked on PGE mineralogy of Kovdor many years ago. Great place to visit, fantastic geology...! Regards, Vlad

Will do, thanks Sarah

Dear Mr. Maqadze,

you explicitly declined to know the classification of gold deposits but want to know how you can classify gold ore.

You can make a desctinction which is intergranular between between hard rock ore (gold ore minerals are intergrown with the gangue minerals) and soft rock ore (gold ore minerals are part of a loose modern placer mineral association or heavy mineral suite with no joint surface of minerals). The other one is intragranular. Visible gold can be spotted as a distinct mineral , whereas invisible gold is accommodated in the structure of certain host minerals such as pyrite or arsenopyrit, as inclusion or part of the lattice).

Best regards

H.G.Dill

Hola Andrea, 

Si no entiendo mal tu pregunta, necesitas una herramienta que te permita gestionar la bibliografía consultada. En este caso, puedes usar el software Mendeley o EndNote. Ambos son muy buenos para organizar información y ayudarte en la escritura de manuscritos.

Saludos.

Sebastian creo que es mejor decirlo en español:

imagina un manto con diamantes que es afectado por un mega-impacto,

como lo sugiere el vídeo.

No digo son diamantes formados por impacto,

digo diamantes de la litosfera Proton o Archon tipo el área de Juina, y si fueron afectadas por un mega impacto?

Cordial saludo

Dear Hugo,

I added a book which includes Cu flowsheet in page 29, and also added to our Cu extraction methods. Sorry about silver.

Best wishes 

I assume you are talking about igneous rocks? Back-arc magmas vary in composition between MORB-like and arc-like, the latter often with quite high K2O contents. Fore-arc rocks are typically low-K.

Dear colleagues:

We need more hard facts. Tidal regimes, volcano-sedimentary sequences, the source of Cr and the host of Cr, as well as  exhalations are very difficult to be put together to give me a coherent picture. Or shall we cast aside the slogan "The present is the key to the past"  for these very old rocks ?  A chemical approach using the V/Cr ratio in the argillaceous layers (so-called fuchsite) may give an answer to the variation in the redox conditions. V increases with lowering of the Eh (more reducing) and Cr responds in the opposite direction (more oxidizing). If it gives a more coherent picture together with barite you get a bit closer to the large-scale environment. I would be very much reluctant to jump too fast into an interpretation of the depositional environment without proper knowledge of the mineralogy and chemistry. Nevertheless, a nice story, to think about.

Best regards

H.G.Dill

SIP from a ground based survey would require a very significant transmitting and receiving electrode spacing with a very large generator.  But it can be done. It's all about geometry and power. 

Dear Mr. Arafa,

I guess you are referring to placer deposits enriched in magnetite, chromite etc. To answer your question it is mandatory primarily whether your goal is more economic or genetic. You have to describe the environment of deposition so as to distil out the proper type of heavy mineral accumulation (eluvial, residual, colluvial, alluvial, fluvial, deltaic, shoreline (lacustrine, marine)). What is the type of commodity to be expected in view of the hinterland ? Is it a proximal or distal placer relative to the potential source rock ? Is it a modern placer-type or a paleo-placer where you might also expect diagenetic overprinting ? What is the age of the host rocks ? There is a wealth of questions to constrain the focal disciplines which come close to the most appropriate one to provide a substantial support to your preparatory work. Otherwise the answer can only be very vague.

Best regards

H.G.Dill

It's important learn to discriminate between shear zones, dykes and others linear features non tectonics. And also, it's important to match your magnetics lineaments with some surface information  (relief lineaments, field data or gammaspectometry map)

You can find some good information here:

GUNN PJ, MAIDMENT D & MILLIGAN PR. 1997. Interpreting aeromagnetic data in areas of limited outcrop. AGSO Journal of Australian Geology and Geophysics, 17(2): 175-185.

Heap leaching if gangue acid consumption is not too high. Whole ore leaching might yield better results. Flotation might yield a smaller plant, but losses from "oxide" (= non-sulphide copper) might be too high. Got to do test work and evaluation to answer properly.

Dear Mr. Beirami

Thanks for your answer.

Best regards

Mansour

Though it is reported to vary from zero to a few thousand ppm Re, and no generalizations are yet possible as to correlations of Re content with geological conditions of formation, .in our experience Rhenium invariably trends with porphyry Mo systems including the Hybrid Climax types that have some base metals such as with copper. . Perhaps it's so as molybdenum invariably breaches the hydrothermal spectrum into much hotter magmatic fancies evidenced by such things as molybdenum with rhenium in Unidirectional Solidification Textures (UST, rhenium having a high melting point, along with molybdenum, not occurring as the free metal but in varies oxidation states, rhenium itself having several) associated with super saturated convective melts brining the magmatic systems from very deep, magma-convectively hot, into the hydrothermal interface and depositions we call "plumes". Interestingly it has one stable isotope, Re185, shared with Indium and tellurium, which occur as rings about hybrid Climax molly porphyry such as the Unicorn deposit. Indium is an indicator of rift environments,  and by inference along with molybdenum and rhenium a direct mantle source into rhyolitic magmas evolved in thick crust of back arc rifts.  

Dear Erik,

Thanks for your comment. Your comment is approved by Dilles and Einaudi (1992).

Dilles, John H., and Marco T. Einaudi. "Wall-rock alteration and hydrothermal flow paths about the Ann-Mason porphyry copper deposit, Nevada; a 6-km vertical reconstruction." Economic Geology 87.8 (1992): 1963-2001.

Kind Regards,

Masoud Ovissi

I think you want to know maximum depth of magnetic anomaly source. Theoretical using down ward method, but this method is unstable. It is better you use from Model Vision software for inversion modelling. The Geosoft is for  data processing, not modeling. Of course, Geosoft has application for  basement Depth Estimation and modeling. Also there are many inversion method or numerical method for final depth estimation.

Good luck

Yes, Dr. Hyseni and Jocelyn, Thank you, this is what I have mentioned and documented in my contribution 4 days ago (see above). Best regards, Anicet

Dear Tharanga,

Here is a copy of a paper that I authored with chemical formula of albite based on EPMA analyses from parent rock minerals in lateritic weathering profiles of Central Africa. Kind regards, Anicet

Dear Perumal,

The positive Eu anomalies indicate strongly weathered gneisses which are high-grade regionally metamorphose granitic rocks. As you know, granites form plagioclase, alkalifeldispar and quartz, and plagioclase make up Ca, Na AlSi3O8, Eu is similar to Ca in therms of ionic characterizations such as Sr,  and Eu takes place of Ca  as diadohy in the crystal structures in the early crystalization stage. This simplified ion exchange process and exhibits diadohy. But in the surface environment, Eu concentrations increase within the sedimentary rocks  by weathered of the Eu rich rocks. This is linking to groundwater/ meteoricwater circulation because of Eh-pH conditions, see attachment files, graphs.

Leyla

Dear Pouria,

here is a link that reviews the techniques for exploring gold placers

and also two doc. that overview different methods for placer exploration in general

Hope these informations will be useful for you

Kind Regards, Anicet

Dear Gary,

Please find enclosed book chapters about Pb isotopes. 

Best wishes

 Hi, perhaps you can try Raster Calculator tools in GIS and 4 band divide 6 band (4/6 ratio). You will receive bitmap. Then you steel have to use Rasret Calculator and formula "bitmap>2" or "bitmap>1.5" (its up to threshold you want). Finally you will receive raster file which you can transform as a shape file, by using "Raster to polyline tools" (or Raster to polygon tolls. its up to you) and you will receive your serpentinites 

Dear Ebot and Dear Guenter,

Many thanks for your suggestions. They were so useful.

Kind Regards,

Masoud Ovissi

Dear Jacob,

I would like to add a comment to the contributions you already have my experience is that a multi disciplinary approach in the key to mineral exploration. Geological mapping and understanding of the structures forms the by the bases for RS. I concur with Richard that the proximity of a mine should not worry you though a mineralised area if close by would definitely  be a plus as Robert has indicated. The principles and processes of remote sensing should be well understood indoor, such that the students can analyse and interpret  an area  without physically going there so that when they carry out ground troothing they already have a picture of what they expect to see. Geomatica and ENVI are some of the good software that one can recommend where you can be able to delineate lineaments ( faults, joints and other linear features ) where mineralisation is most likely to occur. These can also be helpful in identifying alteration haloes  which in some instances are also associated with hydrothermal mineralisation.

Dear Mr. Mikysek,

The identification of the element content of micro grains smaller than 5 microns should not be a big problem.

The bottom line for the use of SEM and EPMA is the surface quality of the samples. The highest surface quality can be achieved with an ion beam cross section polisher. Latest SEM and EPMA analyzers can measure even element profiles in the nanometer range in very sensitive materials.

As an example, I show you here attached a SEM image of an arsenic sulfide surface which has been prepared with an ion beam cross section polisher and was analyzed by an SEM or EPMA quantitatively along a profile line. The tiny spherule (approx. 100 nanometers in diameter) is embedded in a matrix of arsenic sulfide.

Best regards,

Guenter Grundmann

For minerals identification part, you may refer to NASA's JPL Spectral signature library at following links:

You may also refer to my following research work for Dolomite identification from Hyperspectral Imagery. Though, it was an initial research work but it can be useful for the identification of minerals from satellite imagery.

Hope this helps!

As I said any association between intermediate and high sulphidation is quite rare. What you are calling intermediate sulphidation is typical intrusion-related low sulphidation in the earlier Leach and Corbett classification. The Intermediate sulphidation classification as presented in phase diagrams is quite rare in the field and it isn't correct the way the use of the terminology has been expanded. There is a common zonation in these systems from Ag with pyrite sphalerite>galena at depth to a chalcedony dominated assemblages at higher levels, possibly with ginguro. All quite normal as more meteoric waters come in at higher levels and the ore fluids evolve. Have a look at the model presented in figure 9 in the attached paper from the symposium we ran to honour the late Terry Leach. It works better in short course presentations with the rock photos.

Greg

Dear Mr. Aureo,

mining sites which are planned to be rehabilitated must be considered as to the ore which was exploited and the processing applied to separate ore minerals and gangue (trash minerals). Magnetite per se is not a mineral which might cause any bother as it consists of Fe oxide in its tri- and bivalent state. A great deal of the processing used to be carried out using magnetic separation. As far as flotation is involved in depends upon the chemical agents. Considering Ni ore, there are two widespread type Ni sulfide and lateritic Ni ore. Flotation and magnetic separation are part of the processing flow sheet. It is oxidized by roasting and smelted. An Fe-enriched slag is separated from a Cu-Ni matte and later electrolytically refined.

In case of a lateritic Ni ore pyrometallurgical and hydrometallurgical processes are the methods of choice. The intermediate product is later on transferred into Ni matte and ferronickel. Ni is going to be concentrated using ammonia and sulfuric acid.

It is important to know which type of ore was mined and which stage of processing was carried out on site. Based upon this knowledge the means of rehabilitation which are focusing on the pedozone and the hydrozone can be selected.

Best regards

Harald G. Dill

Dear Mrs. Wright,

this is what I expected. Is seems to be a skarnoid mineralization. Have you ever checked your rock slaps under the UV-lamp. I guess scheelite should be detectable. In search of your main gangue minerals I suspect of grandite s.s.s. garnet, vesuvianite (has anomalously blue colors under crossed polars), minerals of the clinozoisite-epidote group or ortho-zoisite (anomalosly blue too under c.p.). The blue color in the image above has definitely not derived from Fe-bearing chlorite, as this phyllosilicate is colorless under ppl. One of your specime which can I not view under a a higher resolution shows uni-directional growth zones and tends to grade into some kind of a wrigglite. Is there a marble or calcareous rock nearby ?

That is for the moment the most far-reaching long-distance diagnosis I dare to give.

Best regards

H.G.Dill

Hi Veiko,

I am interested in  SC5-13f-2015 - EC link: Topic: Strategic international dialogues and cooperation with raw materials producing countries and industry.

Hope you are well and greetings,

Vladimir

Dear Mr. Kumar,

First and foremost it is important to know which part of the alluvial-fluvial drainage system you are considering for stream sediment analysis. Taking samples from the estuaries of the Gulf of Bengal or from the promontory of the Lesser Himalayas makes a difference, I know both.

6000 ppm is high to expect monazite or xenotime as a heavy mineral. If LREE are high monazite is more likely, if Y and HREE are high it is more likely to have to deal with xenotime.

For a review I took the particle size between 63 µm and 630 µm.

After separation with Na-polytungstate, I apply a simple flow sheet -controlled analysis starting with the petrographic microscope (63-300 µm), SEM-EDX/WDX accompanied by XRF. You should carry out a mineralogical and chemical analysis. At an advanced level EMPA and ICP-MS are an option.

Please take a look at some of the paper below and consult for techniques and interpretation:

DILL, H.G., KAUFHOLD, S., LINDENMAIER, F., DOHRMANN, R., LUDWIG, R. and BOTZ, R. (2012) Joint clay-heavy-light mineral analysis: A tool to investigate the hydrographic-hydraulic regime of the Late Cenozoic deltaic inland fans under changing climatic conditions (Cuvelai-Etosha Basin, Namibia).- International Journal of Earth Sciences, 102: 265-304

DILL, H.G., WEBER, B. and KLOSA, D. (2012) Crystal morphology and mineral chemistry of monazite–zircon mineral assemblages in continental placer deposits (SE Germany):Ore guide and provenance marker.- Journal of Geochemical Exploration, 112: 322-346.

DILL, H.G. and KLOSA, D. (2011) Heavy-mineral-based provenance analysis of Mesozoic continental-marine sediments at the western edge of the Bohemian Massif, SE Germany: With special reference to Fe-Ti minerals and the crystal morphology of heavy minerals. - International Journal of Earth Sciences, 100: 1497-1513.

DILL, H.G. (2008) Geogene and anthropogenic controls on the mineralogy and geochemistry of modern alluvial-(fluvial) gold placer deposits in man-made landscapes in France, Switzerland and Germany.- Journal of Geochemical Exploration, 99: 29-60.

DILL, H.G. and LUDWIG, R.-R. (2008) Geomorphological-sedimentological studies of landform types and modern placer deposits in the savanna (Southern Malawi).-Ore Geology Review , 33: 411-434.

DILL, H.G. (2007) Grain morphology of heavy minerals from marine and continental placer deposits, with special reference to Fe -Ti oxides.- Sedimentary Geology, 198: 1-27.

If you cannot download the papers, I can send you privately a copy upon request.

Please let me know the positioning of the sampling sites within the drainage system and the REE variation. Going any further would be a bit of speculation at the moment.

Best regards

Harald G. Dill

Hi Mike:

I would be happy to carry on this discussion outside of the researchgate forum. If you go to my website: www.syngeneticgold.com, you will find several relevant links. In the Noranda-Malartic-Val d’Or corridor, there are many deposits that are clearly synvolcanic. The work of Dick Hutchinson and students addresses some of these and volcanic-hosted gold deposits in general. The Bousquet deposit is generally accepted as synvolcanic. The websites for Virginia Mines (Akasaba deposit); Alto (Destiny Project); Agnico-Eagle (Lapa Deposit) all contain good grade thickness plots from which you can deduct vent geometry. The Val d’Or-Cadillac-Larder Lake Break is a complex stratigraphic interval and not everywhere a fault with displacement and there are several different types of deposits within it. The talc schist in your Figure 2 looks like an altered komatiite and does not present a compelling case that the Pontiac group is faulted against the Piche Group (Legault & Rabeau). One of the most important papers for exploring for syngenetic mineralization is by Phil Thurston, John Ayer et al (2008) in Ec. Geol. They deal with correlative conformities and stratigraphic correlations between authochthonous panels that separate seven discrete volcanic stratigraphic episodes on the basis of groupings of numerous U-Pb zircon ages. Syngenetic concepts have been virtually expunged from the gold deposit literature by articulate epigeneticists. The arguments have been ongoing for 100 years or more, but as we learn more about modern sea-floor hydrothermal systems, we can better understand the Archean equivalents. Also a major breakthrough has come from understanding the role of “lamprophyres”, which is what has compelled me to persist with research on gold deposits. So, I hope syngenetic ideas will be revived again or at least seriously considered instead of continuing to being arbitrarily dismissed or ignored.

I have found accumulation of olivine and pyroxene from a high-Mg basaltic magma (12-13% MgO) in sills as thin as 4m. However, these are not true ultramafic rocks, they are olivine-chromite-enriched melagabbronorites. They also contain minor disseminated sulphides (pyrrhotite-pentlandite-chalcopyrite) which probably formed by contamination of the magma at an earlier stage. These sulphides could possibly contain trace amounts of Pt-Pd sulphides or other PG minerals.

To consider the question of whether the sills nearby to your hydrothermal Pt-Pd deposits could have provided the initial concentration of PGE, there are many things to consider along with the thickness. There is also the stage at which S-saturation occurred (early or late), the sequence of mineral crystallization (olivine-pyroxene-plagioclase, or olivine-plagioclase-pyroxene) and the temperature of magma emplacement (supraliquidus, liquidus, or as a cool, crystal-charged mush).

In order to provide a source for the hydrothermal enrichments, I think that these sills would have to have been emplaced in either a S-undersaturated state, in which case the PGE would have been widely distributed throughout the sill and only weakly concentrated in any mafic-ultramafic cumulate basal layer, or that they were emplaced in a sulphur saturated state, but with the immiscible sulphide droplets still entrained with the magma. In that case, the PGE would all be concentrated into the sulphide droplets, which would be themselves concentrated towards the base of the sills together with olivine-chromite-pyroxene cumulates. The worst case (for pre-enrichment of the PGE in the sills) would be if the magma was already S-saturated, but it had left all or most of the sulphides behind at a deeper level. In that case, the sills would be depleted in the PGE, and would be no better as a source rock for the hydrothermal Pt-Pd than any other crustal rocks like granites, granite-gneisses etc.

Another thing to consider would be the hydrothermal pathways - are the sills themselves or their basal contacts a locus for shearing or any other type of structure permitting fluid ingress?

Dear colleague,

first and foremost your deposit is a carbonate-hosted mineral deposit. You might call it MVT if you like. What is the element association and mineral assemblage, respectively, like? It is decisive to see what the ore traps look like, terms like fractures, faults are not very distinctive and make us speculate too much. In DILL, H.G. (2010) The “chessboard” classification scheme of mineral deposits: Mineralogy and geology from aluminum to zirconium.- Earth Science Reviews, 100: 1-420. There are several color images of carbonate-hosted Pb-Zn-Cu ore types and cross sections. Which of them comes next to yours. Then I can give you some further information. Currently, it seems to be too much of a matter of conjecture.

Excluding barite from MVT or carbonate-hosted deposits is not correct. You find in the cave-in-rock-type a Ba-F-Pb-Zn-(Ag) mineral assemblage, in the Irish type a Ba-Pb-Zn-As-, in the Silesian-type (Ba)-Pb-Zn-(As)- and in the Tunisian-type a Pb-Zn-(Sr-Ba) (celestobarite) mineral assemblage. Some of the largest concentrations of barite are found in calcareous host rocks. It is correct that SEDEX (Rammelsberg, Meggen) have large barite lenses associated with the sulfides. Even VMS deposits have barite- see e.g., Kuroko.

I hope that for the moment it will help you and I am looking forward to your constraints on the ore-type.

Best regards

Harald G. Dill

Romania ranks tenth in the world in terms of the diversity of minerals potential, according the CIA World Fact book

Since the original rocks are probably very altered, I would try to identify the alteration minerals and compare the results with porphyry copper models from other known deposits

These two levels have a regional extending only in Padurea Craiului Mountains . In the Bihor Mountains is a single bauxite level. Have you new and different data?

Mineral Deposits are usually identified through a combination of a set of geoscientific data based on various themes; geological, geochemical, geophysical (both ground and airborne) and remote-sensing (geomorphology, lineament and hyperspectral). Each of these themes characterise a type of information relevant to the mineral deposit of interest. Geospatial modelling techniques using spatial statistics (which also include geostatistical methods like variography and kriging) aim at replicating geological reality as closely as possible, using available geo-information. In addition, refined techniques like stable and radiometric isotope analysis, fluid inclusion study, litho-geochemistry, hyperspectral mapping are combined for generation of genetic/exploration model for the commodity, for effective analysis of the datasets and extraction of only the relevant factors and integration of these factors to generate a single prospectivity map. Integration approaches like conceptual - knowledge driven approach and probabilistic - data driven approach can be used on exploration dataset vis-a-vis its genetic model and construction of prospectivity map that illustrate how mineralization potential or prospectivity changes over an area. The assignment of weightage (interactive / geostatistically) to the various predictor / indicator maps carried out in knowledge driven interactive modelling (Index Overlay, Fuzzy Inference analysis and Vector Fuzzy modelling) and by a quantitative method based on known mineral occurrences with conditional probability following the Bayes rule (Bayesian probability) needs geostatistics in combination with GIS tools. The integration exercise using both 2D map data and 3D borehole data (subsurface geological, geochemical and geophysical) generates prospectivity maps for future exploration target areas. Similar exercise can also help in delineating the extension zones of the already explored ore body.

The integration modelling involves five steps:

• Establish an exploration model

• Build a spatial and related attribute database

• Chose a methodology of data integration – knowledge or data driven

• Process the GIS and attribute data according to methodology

• Apply integration modeling to generate Favourability Maps

The defect density, in quartz at least, seems to be affected by the temperature at which the sample is heated to. This is sensed by way of the sensitivity (amount of luminescence per unit dose) of the resulting OSL. Repetitive heating itself may affect the concentration of charge at point-defects rather than alter their concentration but maybe others may have evidence to the contrary. I believe a more direct way to make this kind of assessment is to use radioluminescence on samples before, during and after the recycling.

The most popular method is mining in pits (depth 2ft - 25ft) and tunnelling. Surface gemming and dredging in river beds are other methods which depend on the nature and the location of the gem deposits. In general, gems are concentrated in a layer of coarse pebble like material with some clay and fine sand. This gem gravel, known as illam is generally found below the alluvial deposits.

Where illam is close to the surface the pits are shallower and circular but the deep pits have a rectangular shape. The scaffolding are made using planks and staves. The space between the staves and earth is stuffed with leaves to prevent walls from collapsing. The water is pumped out by using motors. The tunnelling will be resorted to only if the illam vein runs horizontally. The illam in pits are excavated using crow bars whilst river dredging is done using mammoties. Traditional mining is mainly in a small scale with manpower alone.http://ezinearticles.com/?Gem-Mining&id=7433455