(below is a improved English text compared to the first one published. Thanks to (editing by) Simon McGuinness..!)
The circular economy, is about closing production cycles, is it not? So, it is about restoring the original stock. Otherwise the resource is depleted, and we run out of stock. Yes? But that is precisely what is not discussed in the circular economy approach. No wonder, since its quit disruptive and a long way away from what has been advocated so far. Which is not to say it’s wrong, just that it’s not yet circular. Rather, it is slowing down a linear process. As argued previously.
What happens to date is not about closing the cycle, but about slowing down the degradation of resources on their way to entropy, diluted in the environment, since that’s the natural fate of all resources (unless substantial energy is added, but that’s for later)
It only becomes truly circular if you take responsibility for restoring the original stock. Closing the cycles, so that future generations have the same options available to them and do not have to live on our waste. Especially so, since the same finite pool of resources will have to support more people in the future.
Closing a cycle happens when we replant a tree, after having used one to build a house. In general, this works for biotic or organic resources: these are regrown, naturally or through human intervention (which, in a way, is natural as well, since mankind is part of nature). But it goes further than this, because you will have to insure that the tree is not cut down again until the original mass has been regrown fully, after which the circular process can begin again.
For wood, biomass in general, and water, this circular economy can be easy imagined. But does the same not apply to mineral and metal resources? These also count, in that, the flow impact, is determined by mass, embodied energy and time (speed). Their use can only be circular if the flow of these resources is managed within the regeneration potential of their individual flows. It is only circular if their depletion, or exhaustion, in mass and speed, is no bigger than their natural regeneration capacity. That capacity, the speed by which the deposits are re-formed, may entail many natural processes including photosynthesis, volcanism, or plate tectonics, to name a few.
This also applies for non-biotics, or non-organics, or in circular economy terms: technological sources. The assumption that these do not ‘grow’, or re-form, and that we can’t do anything about this, is wrong, and a misleading framing or reality.
It’s just that it takes very long time, and the per capita flow is meager. There are still new stocks being formed, but at a speed that requires thousands or millions of years. Even oil, gas and coal are still being created, but in amounts that we use up in a fraction of a second. 
If we don’t use more than what is re-constituted by the Earth’s internal processes, then there is no problem. A student from Taiwan once calculated that the whole construction industry in that country could resourced from mountain rocks, without the mountains disappearing: Mountains in Taiwan are pushed up by 2 cm a year, which is more than the local construction industry consumes annually (in terms of mass, based on building mainly in concrete).
For most abiotic (or technical) materials, this timescale is not considered. Thus, there are two options left in that case: either we reduce consumption drastically, to come within the re-concentration capacity of the system, or to re-concentrate the stock ourselves.
About the first option, more later, but first let’s look at reconcentrating or re-storing the stock. Assuming it is impossible to do this, that ‘they are just there’, and ‘found in Nature” , as some argue, is hiding from resource depletion and not taking responsibility. Most current assessment calculations start from that “found” moment, even in scientific research, as in LCA, though research is ongoing as to how to include depletion within LCA. With fossil fuels this is even officially sanctioned: the definition of primary energy starts with resources “as found”. The previous conversions steps are neglected… 
But if we take biotic or organic resources, everyone thinks it is more than obvious to include re-growth into calculations, usually as land use. If we were to argue for treating biotic resources in the same was as we treat abiotic resources, then, trees are just there, “found in nature”. And the forests would rapidly disappear. Just like mineral and metal deposits: there, ready to be taken. This would result in mass protest I assume, if we were to lose all our forests in this way. What is needed here, is a level playing field which ensures the same treatment for all resources. Right now they are not treated equally, which could be seen as “resource racism”: the unequal treatment of resources.
Of course, regeneration of metals and minerals will cost enormous amounts of work, energy, and involve high cost, which is, so far, uncounted. In a capitalistic economy, ( as well as in most circular economy models) the economy profits from the fact that that no responsibility is taken for the stocks, for their depletion and/or exhaustion. To stay within in terms of the Circular economy: ‘re-store’ is also left out of the equation. At least for non-organics. For organics, it is nowadays common to include regrowth (but this is not always the case). There have been many cultures lost in history, for not managing their forests, as we humans learned the hard way.
Since the price and energy demand required to achieve a truly circular approach is enormous, it is obvious that the only attainable and maintainable way of using these resources, is maximizing the use of renewable, biotic or organic materials, also known as bio-based resources. Of course, this use has to stay within our restoring capacity as well. This will inevitably imply that we have to decrease the use of these bio-based resources drastically as well. We will do this by looking for other ways for society to provide such functionalities, without, or with minimal, resource use. Just trying to do better with existing functions, and adding a bit more recycling, won’t do.
Which is yet another deficiency of what is miscalled the circular economy: the focus on a product, regardless of whether that product is produced from renewed or recycled resources. It is not technically wrong, but pointless, when it’s a ‘circular’ process is merely applied for added to a bad solution. That would make it ‘useless re-use’, making the situation even more problematic. Can the product be produced differently, with much less resources? Or can it be provided in another form entirely, as a service for example? We must first consider which option would result in a given functional provision using less resources or make its provision less problematic.
We must also understand that any product or activity might not be permissible anymore, in the light of resource scarcity, or for which we no longer have a budget in terms of CO2 emissions.
So, what is an alternative? I return to my often-used laundry example. A+++ washing machines can be made of recycled materials (maybe), but, even this, is not the solution as we cannot permit ourselves to make 1 billion A+++ recycled washing machines. A laundry-shop is a far better alternative, on a local level with local labor, and with a good pick-up and delivery service creating jobs. This also makes the local system more resilient. For the consumer, the laundry is cleaned and ironed as before, with no difference in the result. Meanwhile, the resources from the old washing machines can be better used for other products: for millions of new wind turbines, for instance.
This kind of strategic thinking based on resource reconstitution is not to be found in the reports going around about the European circular economy. The debate is only about recycling, re-use repair, etc., which is about linear slow down, and how you can make money with that. What is always left out is the steps required for a real circular approach, the Restore approach (as well as Re-think, Re-organise services, etc.). I guess we have the ‘economy’ part to blame for that.
(How to Restore ? : next time. )