We have all read the words “porphyry deposit” and so one should know what it is. My work in geology involved the strength of rock and supporting rock, so I am not trying to pretend I know this topic well, but my understanding is..
This is where a very large intrusion of molten (igneous) rock was rising up from below towards the earth’s surface. It may actually break out on the surface, but often it does not. Due to it’s large size and rounded plug shape, it cools slowly allowing some minerals to grow into large crystals. This leaves a rock with some larger crystals contained within a fine rock mass surrounding them, also known as a porphyry texture. At this time minerals may or may not be concentrating towards the margins. Water percolating down from surface will reach the intrusion and become heated to where it will dissolve minerals and carry them away from the intrusion, something like hot springs activity.
The “hot water” correctly called hydrothermal fluid will also carry Calcium and other elements. This can change the color of surrounding rock. When a person is searching for a mineral deposit, one clue is the greenish signs of hydrothermal alteration.
The end result is a very rare natural occurrence that is awesome from the science involved, but also brings economic significance. The deposit can be several square kilometers in area. It also tends to have a somewhat flat shape and is located close to surface. These are characteristics that make for good mining economics. Good grades, very large volumes. close to surface, and a convenient shape for a mine to follow. It also makes these deposits easier to find than other mineral deposits, and it may well be that there are not very many of these giant sized porphyry deposits remaining undiscovered??
When I first wanted to learn more about Pebble, I went to the company web site and found the linked Sedar page, scrolled down to the first NI 43-101 report which was Feb 6, 2015, and looked for the plan and sections pages 48 to 52. One can see the large size, uniform good grades, and good geometry. Later I would read more, but that alone shows it has the potential to be a world class discovery, without having to rely on the writings and interpretations of others. I find it difficult to understand how some of the critics can be seriously negative, and others will go through the procedure of placing short sell orders, when a person can find proof that the deposit has remarkable characteristics in less than a minute from starting to look for them.
Anyways, take a look at the “2014 Technical Report on the Pebble Project December 31, 2014”