Salt blocks are typically put out during the summer months. Just like we need to replace our electrolytes when we sweat, so do the horses. They typically won't lick more than they need.
In the US, we have county extension offices, they can give you a better idea of what minerals you have in your area. Again, the minerals are much like vitamins that we take, as long as we don't over do it, the body will expel what isn't needed and keep what is needed. Do you have a feed store near you? Sometimes you can fine some good local information there.
Again, check the web out just the first couple of hits when I search basic care for horses http://ayhc.org/pdfs/horse_care.pdf Basic Horse Care Information and Guidelines Basic Horse Care Information
I am really sorry about your first horse. Accidents can always happy but it makes us more nervous the next time. Just trust the knowledge from before. You didn't do anything wrong with the first horse. My horse is outside 24/7 and could be struck by lightning too.
Getting the right horse is much harder than caring for them.