Here is the information from the upcoming Book of Uther concerning iron
Iron
Britain has thirty three iron mines , twenty two of them in Saxon hands in the Perdue Forest, south of London. Three are in the Forest of Dean outside Logres, and two are found in each of Bedegraine, Gloucester, and Brecklands, and one in each of Lonazep and Wuerensis.
Mines are either open pit mines, or extremely dangerous shaft mines. The raw ore is removed from the mine, then is smashed to bits, then washed. The less dense rock washes away, leaving behind the iron. This cleaned ore is then sent to a bloomery.
Bog iron is widespread, and found in many places. The downs, as in Sailsbury, are perfect for finding it. A chemical process leaches iron into masses that are low quality metal, but is a relatively safe and reliable source.
Bloomery, Smeltery
A “bloom” is a twisted spongy chunk of impure iron, and the bloomery is where it is made. Pure ore and charcoal are heated with billows to just below the melting point of iron (1500° C ). Most impurities melt out as slag; what is left is the bloom of impure iron. The quality of the iron varies greatly between blooms, and it all still has some slag in it. About two pounds of iron blooms are made per day, out of 25 pounds of ore. It also requires about 600 pounds of charcoal, which required 6000 pounds of wood. (This shows one reason that nearby forests are so valuable to the process.)
Blooms are distributed or sold to the black smiths, armories and other users of iron.
Smithy, Armory
A smithy turns iron blooms into wrought iron, and then into tools. The blooms must be wrought, or hammered. The smith must choose bits of high and low quality blooms, then heat them together and hammer them into one piece, also knocking out the impurities. The result is called “wrought iron.”
Wrought iron can be made into tools, but high quality tools require multiple rounds of heating and hammering. After fifteen rounds of hammering, the iron is quality steel, suitable for swords.
An Armory is similar but requires a specialist smith who costs £3 per year to maintain.
Bog Iron
Bog iron is found in any fen where water seeps out of the limestone (which has a high iron content) and then into a bog or swamp. These leave small deposits of low-grade “bog iron.” Sources are not regular enough to be commercial, but are often large enough to provide income at the manorial or county level. The Salisbury Plain has such deposits.

I just have to say, this is so interesting! Thank you Greg! And the big reason for thanks is that this answers a lot of questions I've had about iron sources, smeltering and handling for a long, long time. A small portion of this I could've reseached myself, and I do have an excellent material on the local Swedish metal working during the dark ages and later (unfortunately largely unread by me), but to get it all served up like this is invaluable! I live in the "Bergslagen" part of my country, which is the classic area here for mining.

I just have to say, this is so interesting! Thank you Greg! And the big reason for thanks is that this answers a lot of questions I've had about iron sources, smeltering and handling for a long, long time. A small portion of this I could've reseached myself, and I do have an excellent material on the local Swedish metal working during the dark ages and later (unfortunately largely unread by me), but to get it all served up like this is invaluable! I live in the "Bergslagen" part of my country, which is the classic area here for mining.

I've been continuing my research and found a few more mines
Research here means scrutinizing and scribbling all over my Roman Britain map

I just have to say, this is so interesting! Thank you Greg! And the big reason for thanks is that this answers a lot of questions I've had about iron sources, smeltering and handling for a long, long time. A small portion of this I could've reseached myself, and I do have an excellent material on the local Swedish metal working during the dark ages and later (unfortunately largely unread by me), but to get it all served up like this is invaluable! I live in the "Bergslagen" part of my country, which is the classic area here for mining.

I've been continuing my research and found a few more mines
Research here means scrutinizing and scribbling all over my Roman Britain map


Yes, I see. And keep up the good work! That Roman Britain map sounds very interesting. I am a "mappophile" myself so am always keen to see charts, maps and other pictorial descriptions of areas. Maps are also for me such a basic roleplaying need, therefore it confounds me that so many new rpg-makers out there doesn't see it that way. That also includes pictures of how important people/npcs look and other important features. It'a almost like a bad trend these days, with many of the scenario-makers abandoning the pictures. Your material is never lacking there, which is a asset to everyone interested. But I'm getting away from the subject here.

Besides iron, is there going to be material non-agricultural production in Britain and how it might potentially pertain to KAP campaigns?

There's obviously other mining going on. Tin (famously) in Cornwall. I saw something today indicating that silver was discovered near Carlisle in the 12th century and that silver mines in that area were producing 3-4 tons of silver per year in the time period. With lead production as a by-product of the silver production.

You can also branch into quarrying and other industries. Besides local use Purbeck marble* was exported and used in buildings in both London and the various cathedrals in southern England. (* - Not a true marble, but a limestone that did take a polish well.)

In any case it minimally supplies some local flavor to customize an area. For example, a village or market town might not be as productive in terms of grain or sheep, but they have abundant clay and perhaps are known for producing pottery. Or some former Roman quarries are nearby and are still seeing some use. Plus if you're near the sea you have the option for salt-making operations (which is covered in the Book of the Manor.)

Besides iron, is there going to be material non-agricultural production in Britain and how it might potentially pertain to KAP campaigns?

Yes, a little bit
It is primarily important during Anarchy


There's obviously other mining going on. Tin (famously) in Cornwall.

Interestingly, very little tin in Logres
Tin
A little tin is mined in Devon and Tintagel, but the largest mine in Britain is outside Logres, nearby in Dartmoor; and the second largest is south of that in Totnes. They supply 50 tons of ingots for Britain and Europe.
Ore is mined, crushed and then washed to produce “black tin.” Then, in a stannery, it is carefully heated amidst layers of peat. Pure tin melts out, and is cast into ingots.


I saw something today indicating that silver was discovered near Carlisle in the 12th century and that silver mines in that area were producing 3-4 tons of silver per year in the time period. With lead production as a by-product of the silver production.

Lead
Two places in Logres are rich in lead. More fortunate for the king is that lead is just a byproduct of making silver. Thus the income shown is actually for both lead (huge quantities, low price) and silver (rare, high priced).
In Bedegraine, ten mines still operate at Matlock. In Somerset, thirty lead mines are working at Charterhouse [Lutudarum to Romans], in the Mendip hills 10 miles southwest of Bath. These mines used to be the largest supplier of lead and silver in the Roman Empire. The great wealth of Bath [Roman Aqua Sulis] comes from these mines. In ancient times the wise man named Pliney the Elder said, “In Britanniae[lead] is found on the surface in such large quantities that there is a law limiting its production.”
Raw ore is pounded to bits and heated. At one temperature lead separates from the ore. The lead is heated, and the silver separates from it. This is called cupilation.
Silver
The only silver mine in Logres is in Somerset, extracting nearly pure silver. Another is in Totnes, Cornwall.
Silver is mined from deep shafts under dangerous conditions. Slaves work the mine, who are treated badly and replaced as needed. Ore is pounded, rinsed, then melted out, and cast into ingots.
The king takes most of the silver himself to be used for coinage. Quantities are given or sold to the many mints throughout the country. They make silver pennies, the only coin of the realm.


You can also branch into quarrying and other industries. Besides local use Purbeck marble* was exported and used in buildings in both London and the various cathedrals in southern England. (* - Not a true marble, but a limestone that did take a polish well.)

Stone
Four great quarries are under crown control, and provide all Logres with building materials. The king may have granted rights to lords nearby to oversee one of, or part of one of, them. The quarries are Purbeck (Dorset), Box (in Somerset), Barnack (in Lonazep), and Tayton (Clarence). Many smaller quarries are known, and rights belong to the landholder where it is.


In any case it minimally supplies some local flavor to customize an area. For example, a village or market town might not be as productive in terms of grain or sheep, but they have abundant clay and perhaps are known for producing pottery. Or some former Roman quarries are nearby and are still seeing some use.

Not going to bother with clay--to common, not significant for income


Plus if you're near the sea you have the option for salt-making operations (which is covered in the Book of the Manor.)

Salt
Humble salt is critically important to people. It is a table condiment, and is cleaned to be pure white salt for the nobles. Those who sit “below the salt,” by which they mean not at the lord’s end of the table, make do with a brownish salt.
Most importantly, though, salt is the major preserver for fish and meat. Salted cod or herring is a common food for everyone. Bulk salt is shipped inland to every Forester to use in preserving the king’s venison.
[quote]
Suitable coastal areas have salt pans, which are in shallow areas and are used to evaporate seawater. Several inland areas also have rich salt deposits. Anyplace that has the suffix of –wich is a recognized source of salt. These counties have salt: Broadlands, Brecklands, Caercolun, Dorset, Glevum city, Gloucester, Lincoln, Norwich, and Wight.

Welsh Gold ?

Welsh Gold ?

Yes of course
but this is for Logres